1 chem 400 chapter 3 brief intro to chemical bonding

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Chem 400 Chapter 3Chem 400 Chapter 3

Brief Intro to Chemical BondingBrief Intro to Chemical Bonding

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• When atoms react with one another in rxns, the nucleus remains unchanged.

• However, the electrons of the atoms interact, forming chemical bonds to create compounds.

• In other words, electrons are responsible for the chemical properties of substances.

• There are several types of chemical bonds, with the 2 major types being ionic bonds and covalent bonds.

Chemical BondingChemical Bonding

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• A covalent bond is a chemical bond where the electrons of 2 atoms share electrons between the 2 nuclei. The electron clouds overlap, forming the bond.

• In general, covalent bonds form between 2 or more nonmetal atoms or metalloid atoms.

• Chemical substances held together by covalent bonds are called molecules.

Covalent BondingCovalent Bonding

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• Water is a molecule with 2 H atoms covalently bonded to an oxygen atom.

• We can represent a water molecule with a ball and stick model or a space-filling model.

• We can also use structural formulas to represent or draw molecules.


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Representations of MoleculesRepresentations of Molecules

Space-Filling Model

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• Some elements are actually molecules: H2, N2, O2, I2, F2, Cl2, and Br2 are all diatomic molecules or diatomic elements.

• Memorize these 7! Know their formulas!• Notice that although they are molecules, they are

elements, and NOT chemical compounds. (Remember, chemical compounds contain 2 or more DIFFERENT elements.)

• Sulfur exists as S8 while phosphorus exists as P4


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• Ionic bonds are formed when electrons are transferred between 2 atoms.

• 1 atom will give up or lose 1 or more electrons, while the 2nd atom will gain 1 or more electrons.

• Ionic bonds commonly form between metals and nonmetals.

Ions and Ionic BondingIons and Ionic Bonding

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• Atoms which have gained or lost electrons are no longer neutral but have a charge, and so are called ions.

• A cation is a positively charged ion (lost electrons)• An anion is a negatively charged ion (gained

electrons)• We can draw a picture and then write a chemical

equation for the formation of ions:


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Ion FormationIon Formation

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• Once the ions are formed, can you see how the ionic bond is formed?

• What do opposite charges do?

• Equation for formation of NaF, an ionic solid:

Na+ + F- NaF


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• Unlike molecules which are individual discrete compounds, ionic compounds (solids at room temperature) are actually not just 1 cation bonded to 1 anion, but a huge network of cations and anions.

• For example, sodium chloride is NaCl, or table salt. Based on the chemical formula, you might think that there is a unit of 1 Na cation bonded to 1 Cl anion.

• In reality, each Na+ cation is surrounded by 6 Cl- anions, and each Cl- anion is surrounded by 6 Na+ cations.

• These cations and anions are packed close together in what is called a crystal lattice.


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• So why does sodium chloride have the formula NaCl and not Na6Cl6 or as NaxClx?

• The rule is that we express ionic compounds as Empirical Formulas, that is the lowest, most reduced formula.


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• Although many ions are simple monatomic ions, composed of just 1 element, there are also many polyatomic ions.


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• Polyatomic ions are ions containing 2 or more elements. Examples include:

• Polyatomic ions are actually atoms covalently bonded together, but the group of atoms has an overall charge so it is an ion (actually a molecular ion).


NO3- SO4

2- NH4+ OH-

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• The hydrogen cation, H+, the hydroxide anion, OH-,

and the hydronium ion, H3O+, are 3 of the most

important ions in chemistry.

• The reason is that these ions are what defines acid-

base chemistry.

• And H+ is the shorthand notation for H3O+ in

water.

Acids and BasesAcids and Bases

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• The first definition of an acid and base was the Arrhenius Theory:

• Acid: a substance which produces a proton in water

• Ex: HCl, HF, HNO3

• Base: a substance which produces the hydroxide ion in water

• Ex: NaOH, LiOH


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• Notice that in the above examples, the bases are ionic salts as well as bases.

• But the acids are molecules which just happen to "ionize" or lose an H+ in water.

• HCl for example stays intact as HCl in the gas phase.

• HCl readily ionizes to become H+ and Cl- when it is dissolved in water.


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• We show whether an acid or base is dissolved in water or is a gas, liquid, or solid by showing the following notations:HCl(aq) HCl(g) CH3CO2H(l) NaOH(s)

• There are also polyprotic acids, like sulfuric acid, H2SO4, which may lose more than 1 proton when added to water:


H2SO4 (l) H2O⏐ →⏐ ⏐ 2H+(aq) + SO42-(aq)

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• There are also bases which produce more than 1 OH- anion:


Ba(OH)2 (s) H2O⏐ →⏐ ⏐ Ba2+(aq) + 2OH-(aq)

1 chem 400 chapter 3 brief intro to chemical bonding

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