Chapter 9 Models of Chemical Bonding

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ChemicalBondingActivity:化学键合作用

ChemicalBondingActivity:化学键合作用

13 and 14. Make two compounds of lead and sulfur.
Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
5. lead (IV) and nit rogen Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
6. copper (II) and hydroxide ion
Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
In this activity, you will get some practice in learning how atoms form ionic bonds. Listen carefully as the teacher explains the procedure, then begin.
15 and 16. Make two compounds of copper and oxygen.
Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula
3. magnesium and bromine Ion Name
Ion Symbol Anion/Cation How Many? Chemical Formula

Chemical Bonding and Molecular Structure

Chemical Bonding and Molecular Structure

Chemical Bonding and Molecular Structure What Are Chemical Bonds, and Why Do They Form?A chemical bond is the result of an attraction between atoms or ions. The types of bonds that a molecule contains will determine its physical properties, such as melting point, hardness, electrical and thermal conductivity, and solubility. How do chemical bonds occur? As we mentioned before, only the outermost, or valence, electrons of an atom are involved in chemical bonds. Let’s begin our discussion by looking at the simplest element, hydrogen. When two hydrogen atoms approach each other, electron-electron repulsion and proton-proton repulsion both act to try to keep the atoms apart. However, proton-electron attraction can counterbalance this, pulling the two hydrogen atoms together so that a bond is formed. Look at the energy diagram below for the formation of an H–H bond.As you’ll see throughout our discussion, atoms will often gain, lose, or share electrons in order to possess the same number of electrons as the noble gas that’s nearest them on the periodic table. All of the noble gases have eight valence electrons (s2p6) and are very chemically stable, so this phenomenon is known as the octet rule. There are, however, certain exceptions to the octet rule. One group of exceptions is atoms with fewer than eight electrons—hydrogen (H) has just one electron. In BeH2, there are only four valence electrons around Be: Berylliumcontributes two electrons and each hydrogen contributes one. The second exception to the octet rule is seen in elements in periods 4 and higher. Atoms of these elements can be surrounded by more than four valence pairs in certain compounds.Types of Chemical Bonds You’ll need to be familiar with three types of chemical bonds for the SAT II Chemistry exam: ionic bonds, covalent bonds, and metallic bonds. Ionic bonds are the result of an electrostatic attraction between ions that have opposite charges; in other words, cations and anions. Ionic bonds usually form between metals and nonmetals; elements that participate in ionic bonds are often from opposite ends of the periodic table and have an electronegativity difference greater than 1.67. Ionic bonds are very strong, so compounds that contain these types of bonds have high melting points and exist in a solid state under standard conditions. Finally, remember that in an ionic bond, an electron is actually transferred from the less electronegative atom to the more electronegative element. One example of a molecule that contains an ionic bond is table salt, NaCl. Covalent bonds form when electrons are shared between atoms rather than transferred from one atom to another. However, this sharing rarely occurs equally because of course no two atoms have the same electronegativity value. (The obvious exception is in a bond between two atoms of the same element.) We say that covalent bonds are nonpolar if the electronegativity difference between the two atoms involved falls between 0 and 0.4. We say they are polar if the electronegativity difference falls between 0.4 and 1.67. In both nonpolar and polar covalent bonds, the element with the higher electronegativity attracts the electron pair more strongly. The two bonds in a molecule of carbon dioxide, CO2, are covalent bonds. Covalent bonds can be single, double, or triple. If only one pair of electrons is shared, a single bond is formed. This single bond is a sigma bond, in which the electron density is concentrated along the line that represents the bond joining the two atoms. However, double and triple bonds occur frequently (especially among carbon, nitrogen, oxygen, phosphorus, and sulfur atoms) and come about when atoms can achieve a complete octet by sharing more than one pair of electrons between them. If two electron pairs are shared between the two atoms, a double bond forms, where one of the bonds is a sigma bond, and the other is a pi bond. A pi bond is a bond in which the electron density is concentrated above and below the line thatrepresents the bond joining the two atoms. If three electron pairs are shared between the two nuclei, a triple bond forms. In a triple bond, the first bond to form is a single, sigma bond and the next two to form are both pi. Multiple bonds increase electron density between two nuclei: they decrease nuclear repulsion while enhancing the nucleus-to-electron density attractions. The nuclei move closer together, which means that double bonds are shorter than single bonds and triple bonds are shortest of all. Metallic bonds exist only in metals, such as aluminum, gold, copper, and iron. In metals, each atom is bonded to several other metal atoms, and their electrons are free to move throughout the metal structure. This special situation is responsible for the unique properties of metals, such as their high conductivity. Drawing Lewis Structures Here are some rules to follow when drawing Lewis structures—you should follow these simple steps for every Lewis structure you draw, and soon enough you’ll find that you’ve memorized them. While you will not specifically be asked to draw Lewis structures on the test, you will be asked to predict molecular shapes, and in order to do this you need to be able to draw the Lewis structure—so memorize these rules! To predict arrangement of atoms within the moleculeFind the total number of valence electrons by adding up group numbers of the elements. For anions, add the appropriate number of electrons, and for cations, subtract the appropriate number of electrons. Divide by 2 to get the number of electron pairs. Determine which is the central atom—in situations where the central atom has a group of other atoms bonded to it, the central atom is usually written first. For example, in CCl4, the carbon atom is the central atom. You should also note that the central atom is usually less electronegative than the ones that surround it, so you can use this fact to determine which is the central atom in cases that seem more ambiguous. Place one pair of electrons between each pair of bonded atoms and subtract the number of electrons used for each bond (2) from your total. Place lone pairs about each terminal atom (except H, which can only have two electrons) to satisfy the octet rule. Leftover pairs should be assigned to the central atom. If the central atom is from the third or higher period, it can accommodate more than four electron pairs since it has d orbitals in which to place them. If the central atom is not yet surrounded by four electron pairs, convert one or more terminal atom lone pairs to double bonds. Remember that not all elements form double bonds: only C, N, O, P, and S! Example Which one of the following molecules contains atriple bond: PF3, NF3, C2H2, H2CO, or HOF? Explanation The answer is C2H2, which is also known as ethyne. When drawing this structure, remember the rules. Find the total number of valence electrons in the molecule by adding the group numbers of its constituent atoms. So for C2H2, this would mean C = 42 (since there are two carbons) = 8. Add to this the group number of H, which is 1, times 2 because there are two hydrogens = a total of 10 valence electrons. Next, the carbons are clearly acting as the central atoms since hydrogen can only have two electrons and thus can’t form more than one bond. So your molecule looks like this: H—C—C—H. So far you’ve used up six electrons in three bonds. Hydrogen can’t support any more electrons, though: both H’s have their maximum number! So your first thought might be to add the remaining electrons to the central carbons—but there is no way of spreading out the remaining four electrons to satisfy the octets of both carbon atoms except to draw a triple bond between the two carbons. For practice, try drawing the structures of the other four compounds listed. Example How many sigma (s) bonds and how many pi (p) bonds does the molecule ethene, C2H4, contain? Explanation First draw the Lewis structure for this compound, and you’ll see that it contains one double bond (between the two carbons) and four single bonds. Each single bond is a sigma bond, and the double bond is made up of one sigma bond and one pi bond, so there are five sigma bonds and one pi bond. Exceptions to Regular Lewis Structures—Resonance Structures Sometimes you’ll come across a structure that can’t be determined by following the Lewis dot structure rules. For example, ozone (O3) contains two bonds of equal bond length, which seems to indicate that there are an equal number of bonding pairs on each side of the central O atom. But try drawing the Lewis structure for ozone, and this is what you get: We have drawn the molecule with one double bond and one single bond, but since we know that the bond lengths in the molecule are equal, ozone can’t have one double and one single bond—the double bond would be much shorter than the single one. Think about it again, though—we could also draw the structure as below, with the double bond on the other side: Together, our two drawings of ozone are resonance structures for the molecule. Resonance structures are two or more Lewis structures that describe a molecule: their composite represents a true structure for the molecule. We use the double-directional arrows to indicate resonance and also bracket the structures or simply draw a single, composite picture.Let’s look at another example of resonance, in the carbonate ion CO32-:Notice that resonance structures differ only in electron pair positions, not atom positions! Example Draw the Lewis structures for the following molecules: HF, N2, NH3, CH4, CF4, and NO+. Explanation。

Fundmntl Chem 9 ionic&Coval Bond

Fundmntl Chem 9 ionic&Coval Bond

single covalent bonds
or
H
O
H
Double bond – two atoms share two pairs of electrons
O C O
- 8e8e- 8e double bonds
or
O
C
O
double bonds
Triple bond – two atoms share three pairs of electrons
Ionic Bond
Li+ F 2[ 2 [He] Ne] 1s 1s 2s22p6
Li + F
1 22s22p5 1s22s1s
Li e- + Li+ + F F -
Li+ + eF -
Li+ F -
Electrostatic (Lattice) Energy
Lattice energy (E) is the energy required to completely separate one mole of a solid ionic compound into gaseous ions. Q+ is the charge on the cation Q- is the charge on the anion r is the distance between the ions cmpd MgF2 Lattice energy (E) increases as Q increases and/or as r decreases. lattice energy 2957 Q= +2,-1
e- poor

Polar covalent bond (Polar bond)

chemicalBonding化学键解析

chemicalBonding化学键解析
• Ionic bond results from the transfer of electrons from a metal to a nonmetal.
• Metallic bond: attractive force holding pure metals together.
Figure 8.3: Ionic Bonding
+ and the negative pole -.
HyperChem
Drawing Lewis Structures
Follow Step by Step Method (See Ng Web-site)
1. Total all valence electrons. [Consider Charge]
Strengths of Covalent Bonds
Chemical Bonds, Lewis Symbols, and the Octet Rule Lewis Symbols
Chemical Bonds, Lewis Symbols, and the Octet Rule
The Octet Rule • All noble gases except He has an s2p6 configuration. • Octet rule: atoms tend to gain, lose, or share electrons
2. Write symbols for the atoms and guess skeleton structure [ define a central atom ].
3. Place a pair of electrons in each bond.
4. Complete octets of surrounding atoms. [ H = 2 only ]

化学结构英文

化学结构英文

化学结构英文The Chemical StructureChemistry is a fundamental branch of science that delves into the composition, properties, and behavior of matter. At the core of this field lies the concept of chemical structure, which is the arrangement of atoms and their connections within a molecule. Understanding the chemical structure is crucial for comprehending the properties, reactivity, and applications of various substances.One of the fundamental aspects of chemical structure is the arrangement of atoms. Atoms are the basic building blocks of matter, and they consist of a nucleus surrounded by a cloud of electrons. The number and arrangement of protons and neutrons in the nucleus, as well as the number and distribution of electrons, determine the unique characteristics of each element. When atomsof different elements combine, they form molecules, and the specific way in which these atoms are arranged within the molecule is known as the chemical structure.The chemical structure of a molecule can be represented using various models, such as the ball-and-stick model, the space-fillingmodel, and the line-angle model. The ball-and-stick model depicts atoms as spheres connected by sticks, representing the chemical bonds. The space-filling model, on the other hand, shows the relative size and shape of the atoms in the molecule, providing a more accurate representation of the overall structure. The line-angle model is a simplified representation where atoms are shown as points, and the bonds between them are represented by lines or angles.The arrangement of atoms within a molecule is governed by the principles of chemical bonding. There are several types of chemical bonds, including covalent bonds, ionic bonds, and hydrogen bonds. Covalent bonds are formed by the sharing of electrons between atoms, and they are the most common type of bond in organic chemistry. Ionic bonds are formed by the transfer of electrons from one atom to another, resulting in the formation of positively and negatively charged ions. Hydrogen bonds, on the other hand, are a special type of intermolecular interaction that occurs between a hydrogen atom and a highly electronegative atom, such as oxygen or nitrogen.The chemical structure of a molecule also determines its overall shape and geometry. The shape of a molecule is influenced by the number and type of bonds, as well as the arrangement of the atoms around the central atom. The most common molecular geometriesinclude linear, trigonal planar, tetrahedral, and octahedral, among others. These geometric arrangements have a significant impact on the physical and chemical properties of the molecule, such as its polarity, reactivity, and intermolecular interactions.The understanding of chemical structure is crucial for many practical applications in various fields, including medicine, material science, and environmental science. In the field of medicine, the chemical structure of drugs plays a crucial role in determining their effectiveness and potential side effects. Researchers and pharmaceutical companies use this knowledge to design and develop new drugs that target specific biological processes. In material science, the chemical structure of materials is essential for understanding and manipulating their properties, such as strength, flexibility, and conductivity, which are crucial for the development of new technologies.Moreover, the chemical structure of molecules is also important in environmental science, as it can help in understanding and addressing environmental issues. For example, the chemical structure of pollutants can provide insights into their behavior, fate, and potential impact on the environment, which is crucial for developing effective strategies for environmental remediation and protection.In conclusion, the chemical structure is a fundamental concept inchemistry that underpins our understanding of the composition, properties, and behavior of matter. By studying the arrangement of atoms and their connections within molecules, scientists can gain valuable insights into the natural world and develop innovative solutions to various challenges facing humanity.。

Chapter 8 Concepts of Chemical Bonding - John Bowne High School:8章概念的化学键-约翰邦恩高中精品文

Chapter 8 Concepts of Chemical Bonding - John Bowne High School:8章概念的化学键-约翰邦恩高中精品文
• The energy associated with electrostatic interactions is governed by Coulomb’s law:
Eel =
Q1Q2 d
Chemical Bonding
• Lattice energy depends on the charges of the ions and the sizes of the ions
Chemical Bonding
Step
1 2 3 4 5
Energetics
Chemical Bonding
Step
1 2 3 4 5
Energetics
endothermic endothermic endothermic Exothermic Exothermic (highly)
Chemical Bonding
Chemical Bonding
Energetics of Ionic Bonding
• There must be a third piece to the puzzle.
• What is as yet unaccounted for is the electrostatic attraction between the newly formed sodium cation and chloride anion.
is a constant (8.99 x 10 9 J·m/C2), Q1 and Q2 are the charges on the ions, and d is the distance between ions.
Lattice energy increases as * The charges on the ions increase * The distance between the ions decreases.

Chapter 9-aromatic

Chapter 9-aromatic
该理论认为苯环中未参与成键的p电子均
指向分子的中心,这样每个键在反应时具 有潜在的能量,则6个碳-碳键由于能量 相同而有相等的键长。但该理论强调该结 构仅存在于芳香族化合物中。该模型可解 释苯分子中六个碳碳键长相等,苯的一元 及邻二卤代物只有一种,但对定位规律的 解释不是很理想。
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悌勒的余价学说
17
(2)共振结构式的书写 a,必须符合价键规则。
b,只允许键合电子(π电子和孤对电子) 移动,不允许原子排列顺序发生变化。 .. + CH3O-CH=CH2 CH3O=C-CH2 CH2=CH-OH CH3CHO CH2-CH2 CH2
在所有极限结构中,配对的或不配对电子数目应保持一致
18
CH2=CH-CH2
该理论认为苯分子中的双键不是成键的p电
子全部成键,而是还剩一点,重新组合并 在单键间成键,从而使苯中的单双键的键 长相同。
除了以上两种设想外,还有拉登堡的三棱柱结构
、德瓦尔苯结构
、富烯结构
这些新提出的结构都想弥补凯库勒式的不足。但 却都不及凯库勒式,目前,广泛应用的仍是凯库 勒式,也叫凯库勒经典式。
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9.1.4 An Orbital View of Benzene
Structure is planar, hexagonal. C–C–C bond angles 120° All its C-C bonds are the same length: 139 pm — between single (154
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9.1.2 苯的其它结构的设想
为了补充苯的凯库勒结构式的这些不足,人们
以相继提出有关苯的其它的结构和设想。如其 它的结构解释还有 盖尔的中心键理论 悌勒的余价学说 价键理论(现代的解释方法) 分子轨道理论(现代的解释方法) 共振论(现代的解释方法)等

Chemical Bonding

Chemical Bonding

Lewis Structures

Elements with 2 valence electrons are called the Alkaline Earth metals (group 2) (Label)
Lewis Structures

Elements with 7 valence electrons are called the Halogens (group 7) (Label)
+1
-2 0
Nitrogen? -3
Charges
Charges

A few exceptions!


Metals are always a positive charge!! Non metals are always negative!! Metalloids can go either way (you are not responsible for choosing – I will tell you) According to rule of 4’s….its a +3 charge But since it’s a nonmetal, we use -5!
Ionic Bonds




Usually formed by members of the Alkali group (ones with +1 electron) Electrons are donated to another molecule Between elements from opposite sides of the chart Forms crystals (salts) & most dissolve in water

chapter7-ChemicalBonding(化学链接)

chapter7-ChemicalBonding(化学链接)

价键为两原子共享电子对之化学键,其结合原子皆为非金属原子
Covalent compound H2, Cl2
4
Ionic Compound 离子化合物
Solids
Covalent Compound 共价化合物
Gases, liquid, or solids
High melting points (>400oC)
• An ion is an atom or a group of atoms possessing a net electrical charge. • Ions come in two basic types: – positive (+) ions or cations
•These atoms have lost 1 or more electrons.
5 electrons in valence shell
Not as useful for the transition and inner transition elements 7 (不适用于过渡元素)
Ionic Bonding 离子键结 Formation of Ionic Compounds 形成离子化 合物
• NH4+ ammonium ion -- cation • NO2-, CO32-, SO42- sulfate ion – anions
9
Ionic Bonding is the attraction of oppositely charged ions (cations and anions) in large numbers to form a solid. Such a solid compound is called an ionic solid.

The Study of Chemical Bonding Theories

The Study of Chemical Bonding Theories

The Study of Chemical Bonding Theories 化学键合理论研究化学键是一种将原子结合在一起的力量,在化学反应中起至关重要的作用。

化学家们一直在探索研究化学键的本质和机理,形成了许多化学键合理论。

本文将介绍一些较为常见的化学键合理论以及它们的原理和应用。

共价键理论共价键理论是指共用一对电子对于元素之间的化学键形成。

该理论由保罗·卡扎罗夫(Pauling)于1931年提出。

根据该理论,元素之间的化学键形成是通过原子之间的电子进行互相共享以达到最稳定的状态。

这种共用电子对使得互相结合的元素之间能够共享起来一份电子,从而形成一种共价键。

轨道杂化理论轨道杂化理论是指原子在形成共价键时,由于需要构建新轨道,从而发生原子内轨道的重组。

这种重组后的轨道称为杂化轨道。

该理论是由瓦伦丁·范特·霍夫(Valentine van't Hoff)和皮尔斯(G.N.Lewis)等人提出。

分子轨道理论分子轨道理论(MO理论)是指利用量子力学来研究分子结构和化学键的一种理论。

根据该理论,分子中的电子并不是单独存在于原子之间,而是形成了一种共同的电子云。

这种共同的电子云中的电子轨迹称为分子轨道。

通过对分子轨道进行研究,可以得出分子的稳定性和可能的反应情况。

离子键理论离子键理论是指在离子化合物中,物质之间的结合是由于有正负离子之间的静电作用力所导致的。

由于正负离子之间的吸引力足够强,从而形成了一种离子键。

金属键理论金属键理论是指金属元素在形成化学键时,通过共用它们结构中的空穴轨道,从而形成了一种金属键。

这种金属键的力量比较弱,因此也容易被打破。

总的来说,化学键合理论的研究不仅深化了我们对化学反应的认识,而且还为我们探索和设计新的化学反应提供了更多的可能性。

化学家们也正在不断努力进行更深入的研究,更好地理解并应用这些理论。

ChemicalBonding化学链接ppt课件

ChemicalBonding化学链接ppt课件
➢ Ionic bonding 离子键结 results from electrostatic attractions among ions, which are formed by the transfer of one or more electrons from one atom to another.
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Chemical Bonding 化学键结
精选版课件ppt
1
Chapter Goals
1. Lewis Dot Formulas of Atoms 路易斯电子点结构式
Ionic Bonding 离子键结
2. Formation of Ionic Compounds 形成离子化合物
Covalent Bonding 共价键结
子拉进的吸引力称之为化学键结)
• The electrons involved in bonding are usually those in the outermost (valence) shell (与键结有关的电子通
常是指最外层的电子)
精选版课件ppt
3
Introduction
• Chemical bonds are classified into two types:
– negative (-) ions or anions
•These atoms have gained 1 or more electrons.
精选版课件ppt
8
Formation of Ionic Compounds
• Monatomic ions consist of one atom.
– Examples:
Low melting points (<300oC)

CHEMICALBONDINGYaleDepartmentofChemistry:化学键耶鲁大学化学

CHEMICALBONDINGYaleDepartmentofChemistry:化学键耶鲁大学化学
1
CHEMICAL BONDING
Cocaine
2
Chemical Bonding
Problems and questions —
How is a molecule or polyatomic ion held together?
Why are atoms distributed at strange angles?
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Electron Distribution in
Molecules
G. N. Lewis 1875 - 1946
• Electron distribution is depicted with
Lewis electron dot structures
• Valence electrons are distributed as
valence electrons
B 1s2 2s2 2p1 Core = [He] , valence = 2s2 2p1
Br [Ar] 3d10 4s2 4p5 Core = [Ar] 3d10 , valence = 4s2 4p5
Rules of the Game
11
No. of valence electrons of a main group atom = Group number
Chemical Bonding:
6
Objectives
Objectives are to understand:
1. valence e- distribution in molecules and ions.
2. molecular structures
3. bond properties and their effect on molecular properties.

第九版生物化学与分子生物学

第九版生物化学与分子生物学

第九版生物化学与分子生物学英文回答:Biochemistry and molecular biology are two closely related fields that study the chemical processes and molecules that are essential for life. These disciplines provide insights into the fundamental mechanisms of living organisms at the molecular level. In biochemistry, we investigate the chemical reactions and pathways that occur within cells, while molecular biology focuses on the structure and function of biomolecules such as DNA, RNA, and proteins.Biochemistry plays a crucial role in understanding how cells function and how diseases develop. For example, the study of enzymes, which are proteins that catalyze biochemical reactions, helps us understand metabolic pathways and how they can be disrupted in diseases such as cancer. By studying the structure and function of biomolecules, molecular biology provides insights into howgenetic information is stored, transmitted, and expressed. This knowledge is essential for developing new treatments and therapies for genetic disorders.One of the major advancements in biochemistry and molecular biology is the development of techniques for DNA sequencing. The ability to sequence the entire genome of an organism has revolutionized our understanding of genetics and has opened up new possibilities for personalized medicine. For example, by sequencing an individual's genome, we can identify genetic variations that may increase their risk of developing certain diseases. This information can then be used to develop targeted therapies or preventive measures.Another important area of research in biochemistry and molecular biology is the study of protein structure and function. Proteins are involved in almost every biological process and understanding their structure allows us to understand how they carry out their functions. This knowledge is crucial for drug discovery and development, as many drugs target specific proteins to treat diseases. Forexample, the development of drugs that target specific proteins involved in cancer cell growth has revolutionized cancer treatment and improved patient outcomes.In conclusion, biochemistry and molecular biology are interdisciplinary fields that provide insights into the chemical processes and molecules that are essential forlife. These fields have revolutionized our understanding of genetics, disease mechanisms, and drug development. The advancements made in these fields have paved the way for personalized medicine and have the potential to greatly impact human health.中文回答:生物化学和分子生物学是两个紧密相关的领域,研究生命必需的化学过程和分子。

Understanding the Mechanism of Chemical Bonding

Understanding the Mechanism of Chemical Bonding

Understanding the Mechanism ofChemical BondingChemical bonding is a fundamental concept in chemistry that explains how atoms combine to form molecules. It is based on the idea that atoms are held together by attractive forces that can be described as chemical bonds. The understanding of chemical bonding is important for predicting the behavior of materials and developing new compounds for various applications. In this article, we will discuss the mechanism of chemical bonding and the different types of bonds that exist.The Mechanism of Chemical BondingThe mechanism of chemical bonding can be explained by the quantum mechanical model of the atom. According to this model, electrons are arranged in energy levels or orbitals around the nucleus of an atom. Each orbital can hold a maximum of two electrons, and electrons in the same orbital have opposite spins. The energy of the orbitals increases as the distance from the nucleus increases.When two atoms approach each other, their electron clouds interact and create a region of space called the molecular orbital. In this region, the atoms share electrons and form a chemical bond. The nature of the chemical bond depends on the way the electrons are shared.Types of Chemical BondsThere are three major types of chemical bonds: ionic, covalent, and metallic.Ionic bonds occur between atoms with large differences in electronegativity. Electronegativity is the measure of an atom's ability to attract electrons towards itself. In an ionic bond, one atom transfers electrons to another atom to form ions. The positively charged ion is called a cation, and the negatively charged ion is called an anion. The attraction between the opposite charges of the ions creates the ionic bond. Ionic bonds are typically found in salts and other compounds containing metals and non-metals.Covalent bonds occur between atoms with similar electronegativity. In a covalent bond, atoms share electrons to form a molecule. The sharing of electrons is unequal in some cases, leading to polar covalent bonds. In a polar covalent bond, the electrons are shared unevenly due to unequal electronegativity. The more electronegative atom attracts the electrons towards itself, creating a partial negative charge. The less electronegative atom has a partial positive charge. Covalent bonds are common in organic molecules and many other compounds.Metallic bonds occur between atoms of metals. In a metallic bond, the outermost electrons of the metal atoms are delocalized. This means that the electrons are not bound to any particular atom, but rather move freely throughout the metal lattice. The delocalized electrons are responsible for the properties of metals such as conductivity, malleability, and ductility.ConclusionIn conclusion, chemical bonding is a fundamental concept in chemistry that explains how atoms combine to form molecules. The mechanism of chemical bonding is based on the quantum mechanical model of the atom, which describes how electrons are arranged in energy levels around the nucleus. There are three major types of chemical bonds: ionic, covalent, and metallic. Understanding the different types of bonds is important for predicting the behavior of materials and developing new compounds for various applications.。

The Dynamics of Chemical Bonds and Reactions

The Dynamics of Chemical Bonds and Reactions

The Dynamics of Chemical Bonds andReactionsChemical bonds and reactions are integral components of the field of chemistry, which is concerned with the composition, structure, properties, and reactions of matter. Chemical bonds are the forces that hold atoms and molecules together, while chemical reactions involve the breaking and formation of bonds to create new substances. The study of these phenomena is essential to our understanding of the natural world and has practical applications in fields such as medicine, materials science, and environmental science.The Formation of Chemical BondsThe formation of chemical bonds is a complex process that involves the interaction of electrons. The electrons in an atom occupy different energy levels or orbitals, with those in the outermost shell being the most important for bonding. Atoms can form chemical bonds by either transferring or sharing electrons with other atoms. In ionic bonding, an electron is transferred from one atom to another, resulting in the formation of ions with opposite charges that attract each other. This type of bonding is observed in compounds such as sodium chloride (NaCl). In covalent bonding, atoms share electrons to form a stable molecule. This type of bonding is observed in compounds such as water (H2O).The Strength of Chemical BondsThe strength of a chemical bond depends on several factors, including the type of bond, the electronegativity of the atoms involved, and the distance between them. Ionic bonds tend to be stronger than covalent bonds, as the electrostatic attraction between ions is greater than the sharing of electrons. In covalent bonds, the greater the difference in electronegativity between the atoms, the stronger the bond. For example, the bond between hydrogen and oxygen in water is stronger than the bond between hydrogen and carbon in methane (CH4). The distance between the atoms also affects the strength of thebond, with shorter distances resulting in stronger bonds due to the increased attraction between the nuclei and the shared electrons.Chemical ReactionsChemical reactions involve the breaking and formation of chemical bonds to create new substances. A chemical equation represents a reaction, with the reactants on the left-hand side and the products on the right-hand side. Reactants are the starting materials, while products are the substances that are formed. Chemical reactions can be classified into different types based on the nature of the reaction, such as combustion, oxidation-reduction, and acid-base reactions.Energy Changes in Chemical ReactionsChemical reactions involve the transfer of energy, which can either be absorbed or released. Endothermic reactions absorb energy, while exothermic reactions release energy. The energy change in a reaction can be measured using a technique called calorimetry, which involves measuring changes in temperature. The enthalpy change (∆H) of a reaction is a measure of the energy involved and is positive for endothermic reactions and negative for exothermic reactions.Factors Affecting Chemical ReactionsSeveral factors can affect the rate of a chemical reaction, including temperature, concentration, surface area, and catalysts. Increasing the temperature of a reaction generally increases the rate of the reaction, as it provides more energy to the particles involved, which increases their kinetic energy and the likelihood of successful collisions. Increasing the concentration of reactants also increases the rate of a reaction, as it provides more particles for collisions. Similarly, increasing the surface area of reactants increases the rate of the reaction, as it provides more contact between the particles. Catalysts are substances that can speed up chemical reactions by lowering the activation energy required for the reaction to occur. Catalysts provide an alternative pathway for the reaction, which requires less energy for the bonds to be broken and formed.ConclusionIn conclusion, the dynamics of chemical bonds and reactions are essential to our understanding of the natural world and have practical applications in fields such as medicine, materials science, and environmental science. The formation of chemical bonds involves the interaction of electrons, with ionic bonds involving the transfer of electrons and covalent bonds involving the sharing of electrons. The strength of a chemical bond depends on several factors, including the type of bond, the electronegativity of the atoms involved, and the distance between them. Chemical reactions involve the breaking and formation of chemical bonds to create new substances, with energy changes occurring in the process. The rate of a chemical reaction can be affected by several factors, including temperature, concentration, surface area, and catalysts.。

化学英语教案高中必修二

化学英语教案高中必修二

化学英语教案高中必修二Topic: Chemical BondingObjective:- To understand the concept of chemical bonding and its importance in forming compounds - To classify different types of chemical bonds, including ionic, covalent, and metallic bonds - To demonstrate how to write Lewis dot structures for different compounds- To explain the relationship between bond strength and compound stabilityMaterials:- Whiteboard and markers- Models of atoms and molecules- Worksheets for Lewis dot structures- Safety goggles for all studentsIntroduction:In this lesson, we will be discussing the concept of chemical bonding, which is essential for understanding how elements combine to form compounds. Chemical bonding is the process where atoms are held together in a compound by attractive forces. There are three main types of chemical bonds: ionic, covalent, and metallic bonds. Each type of bond has its own characteristics that determine the behavior of the compound.Instructional Strategies:1. Start the lesson by reviewing the basic structure of an atom and the concept of valence electrons. Emphasize the importance of valence electrons in determining how atoms bond with each other.2. Introduce the concept of ionic bonding, where atoms transfer electrons to achieve stability. Use models to demonstrate how atoms of different elements bond to form ionic compounds.3. Discuss covalent bonding, where atoms share electrons to achieve stability. Show examples of covalent compounds and explain how to write Lewis dot structures to represent covalent bonds.4. Explain metallic bonding, where electrons are free to move throughout a metal's structure. Discuss the unique properties of metals and how metallic bonds contribute to these properties.5. Have students complete worksheets on writing Lewis dot structures for different compounds to practice their understanding of chemical bonding.6. Conduct a class discussion on the relationship between bond strength and compound stability. Emphasize how the type of bond affects the properties of a compound. Assessment:- Have students complete a quiz on the different types of chemical bonds and their characteristics.- Assign a homework assignment where students have to identify the type of bond in various compounds and explain their reasoning.- Evaluate students' understanding of chemical bonding through class participation and discussions.Conclusion:By the end of this lesson, students should have a clear understanding of the different types of chemical bonds and how they contribute to the formation and properties of compounds. Understanding chemical bonding is crucial for students to grasp the fundamentals of chemistry and further explore the intricate world of atoms and molecules.。

The Formation of Chemical Bonds

The Formation of Chemical Bonds

The Formation of Chemical BondsChemical bonds are the forces that hold atoms together in a molecule or compound. Without chemical bonds, the world as we know it would not exist. From the water we drink to the air we breathe, chemical bonds play a crucial role in our daily lives.The formation of chemical bonds can be understood through the concept of electron sharing. In simpler terms, chemical bonds are formed when two or more atoms share electrons with each other.Covalent Bonding:The most common way that atoms form a bond is through covalent bonding. Covalent bonds occur when two atoms share one or more pairs of electrons. This type of bonding is common in molecules such as water, because each hydrogen atom shares one pair of electrons with the oxygen atom.Ionic Bonding:Ionic bonding occurs when one or more electrons are transferred from one atom to another to form ions. The resulting attraction between these ions creates a strong bond. An example of an ionic bond is the bond between sodium and chlorine in table salt.Metallic Bonding:Metallic bonding is unique to metals and occurs when metal atoms share their electrons with each other. This creates a pool of electrons that can move freely throughout the metal, giving it its characteristic properties such as malleability and conductivity.Intermolecular Forces:While chemical bonds hold atoms together within a molecule or compound, intermolecular forces hold molecules or compounds together. These forces are weaker than chemical bonds but are still important to the properties of a substance. For example,intermolecular forces hold water molecules together to form a liquid, and are also responsible for the surface tension of water.The formation of chemical bonds is critical to the functioning of our world. It is responsible for the diversity of substances and the properties they exhibit. Without chemical bonds, the world would be vastly different, and life as we know it would not be possible.。

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