Chapter 7 and 8Ionic and Covalent Bonding

7.1 Ions• Valence Electrons are the electrons in

the highest occupied energy level of an element’s atoms.

• The number of valence electrons determines the chemical properties of an element.

• To find the number of valence electrons in an atom of a representative element, look at the group number. (see table 7.1)

Valence Electrons

• Valence electrons are usually the only electrons used in chemical bonds, so they are show in electron dot structures.

• In forming compounds, atoms tend to achieve the electron configuration of a noble gas.

• This is called the Octet Rule.

• All atoms want to have 8 electrons in their outer or valence shell.

Formation of Cations

• Atoms of the metallic elements tend to lose their valence shell electrons leaving 8 in the next level down.

• An atom’s loss of valence of electrons produces a cation, or positively charged ion.

• Remember, an ion is a charged atom that has lost or gained electrons during the chemical bonding process.

Na

Neutral Sodium Atom

+Whoa…I just got smaller…

Cl

Neutral Chlorine Atom

-Now I’m bigger and stronger….

Transition Metals

• For transition metals, the charges of cations may vary.

• For example, elements such as iron, nickel and copper may lose 1 to three electrons depending on the chemical compound.

Formation of Anions• A anion is an atom or group of atoms with a

negative charge.

• The gain of a negatively charged electron by a neutral atom will create an anion.

• Non-metals typically form anions.

• The name of the anion is not the same as the name of the atom.

• It usually ends in –ide. (See table 7.2)

Vocabulary Cards

• Valence electron

• Octet Rule

• Transition Metal

SUM IT UPName the following ions properly.

F-

Cl-

Ca+2

O-2

Electron Configurations

• An electron configuration is a way to show the electrons in a particular atom in the proper order.

• Since electrons are arranged in shells, each shell has a different name.

• Use the periodic table to figure out the electron configuration for any atom.

LET’S PRACTICE!

1s2 2s1

1s2 2s2 2p5

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3

Vocabulary Cards

• Electron configuration

POST IT UP

What is the electron configuration for carbon?

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7.2 Ionic Bonds and Ionic Compounds

• Compounds composed of cations and anions are called ionic compounds.

• Ionic compounds are usually composed of a a metal and other nonmetals.

• Although they are composed of ions, they are electrically neutral…meaning no charges or their charges cancel out.

• Bonds that hold ionic compounds together are called ionic bonds.

Formula Units

• A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance.

• A formula unit is the lowest whole-number ratio of ions in an ionic compound.

• The chemical formula is not always the lowest whole number ratio.

Let’s Practice

• How many kinds of atoms are in each of these ionic compounds?

• NaCl

• MgCl2• Ca(OH)2

• Ca3(PO4)2

Properties of Ionic Compounds

• Most ionic compounds are crystalline solids at room temperature.

• Ionic compounds generally have high melting points.

• Ionic compounds can conduct an electric current when melted or dissolved in water.

Vocabulary Cards

• Ionic Bond

• Formula Unit

SUM IT UP

How many kinds of each of these atoms are in this compound?

Ca (C2H6O2)2

8.1 Molecular Compounds.• Some compounds are not ionic.• Instead of giving or taking electrons, these

compounds share electrons to complete their Octet.

• This is called a covalent bond.• A molecule is a neutral groups of atoms joined by

a covalent bond.• A diatomic molecule is a molecule consisting of

only two atoms.• A compound composed of molecules is called a

molecular compound.

Molecular Formulas

• A molecular formula is the chemical formula of a molecular compound.

• It shows how many of each element a molecule contains.

• A molecular formula does not tell you about a molecule’s structure.

8.2 The Nature of Covalent Bonding

• In forming covalent bonds, electron sharing usually occurs so that atoms attain the electron configuration of a noble gas.

• Combinations of nonmetallic elements in groups 4A, 5A, 6A and 7A are likely to form covalent bonds.

• They share electrons to achieve an octet like a noble gas.

Diagrams• An electron dot diagram represents the

shared pairs of electrons in a molecule.

• Each bond is two electrons or two dots.

• A structural formula represents the covalent bonds by dashes and shows the arrangement of the atoms.

• Each dash will equal two electrons.

• A pair of valence electrons not shared between atoms is called an unshared pair, lone pair or nonbonding pair.

Lone unshared pairs

Polyatomic ions

• A polyatomic ion is a tightly bound group of atoms that has a positive or negative charge and behaves like a unit.

• A group of atoms may be covalently bonded as a polyatomic ion but since the whole unit has a charge, it can bond with other charged ions.

Vocabulary Cards

• Covalent bond

• Molecule

• Polyatomic ion

• Unshared pair

SUM IT UP

Draw the structural diagram for water.

8.4 Polar Bonds and Molecules• Covalent bonds involve sharing between atoms.• However, some atoms are more electronegative

than others meaning they tend to attract more electrons than other atoms.

• When all the electrons are shared equally, it is a nonpolar covalent bond.

• When one atom attracts electrons more strongely than the other atom, a polar covalent bond forms.

• The atom that attracts more electrons become slightly negative while the other becomes slightly positive.

• This is NOT the same as an ionic bond with normal charges!

Hydrogen Bonds• Hydrogen bonds occur when a hydrogen that

is covalently bonded to another atom will be weakly attracted to another atom on another molecule.

• The partial positive charge of the hydrogen in the polar molecule, gets attracted to the partially negative charge on another molecule.

• Water usually forms hydrogen bonds.

• As a result, life is possible.

Vocabulary Cards

•Polar molecule

•Hydrogen bond

POST IT UP

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Why is water polar?

Science Swag

Create an accurate model for a chemical compound. Label the atoms and the bonds. Bigger models with more atoms get more points.