Compounds, Ions, and Molecules

• Compounds result when elements

bond together in fixed proportions.

• Bohr diagrams can illustrate how ions form by focusing on the

atom’s electrons.

• Atoms tend to acquire the same number of valence electrons as

their nearest noble gas.

7CHAPTER

Compounds, Ions, and Molecules

• A chemical bond (a force that holds atoms

together to form compounds) can involve

electron transfer or electron sharing.

• Ionic bonds involve a transfer of electrons

between atoms. Ionic bonding forms ionic

compounds.

• Covalent bonds involve a sharing of

electrons between atoms. Covalent bonds

form molecular compounds.

• Rules for writing chemical formulas and for

naming ionic compounds are based on ion

charge balances.

• Example: The chemical formula for sodium

oxide is Na2O.

7CHAPTER

Compounds, Ions, and Molecules

• Rules for writing chemical formulas and for naming molecular

compounds are based on a prefix system. Ionic bonds involve a

transfer of electrons between atoms. Ionic bonding forms ionic

compounds.

• Molecular compounds result when atoms of non-metals bond by

sharing electrons.

7CHAPTER

Compounds, Ions, and Molecules

Activity• In chapter 6, we looked at chemical families (the columns) in the Periodic

Table.

• In pairs, examine columns 1, 2, 16, and 17. Determine how many electrons each element would lose or gain to have the same number of electrons as its nearest noble gas.

• Do you notice a pattern within the chemical families?

• What generalizations can you make about the families and the ions they may form?

• Can you predict the ions group 13 elements will form?

• Confirm your predictions using the textbook (pages 172–173).

7CHAPTER

Compounds, Ions, and Molecules7

Key Ideas

• Compounds result when elements bond together in fixed

proportions.

• Bohr diagrams can illustrate how ions form.

• Bonding can involve electron transfer (ionic) or electron sharing

(covalent).

• Rules for writing chemical formulas and for naming ionic

compounds are based on ion charge balances.

• Rules for writing chemical formulas and for naming molecular

compounds are based on a prefix system.

CHAPTER

• The simplest form of matter is an element.

• The smallest particle of an element is an atom.

• Some elements like to combine, or bond, to form

compounds in fixed proportions.

• For example NaCl and H2O are compounds.

• Each compound has properties that are different than those of the

elements they are composed of.

• For an element, the tendency to bond or form an ion is determined by

the number of electrons in its outermost shell called the valence shell.

• Bohr diagrams focus on the valence electrons.

Compounds, Atoms, and Ions7.1

VOCABULARY

bond

valence shell

valence electron

ion

• Atoms tend to acquire the same number of valence

electrons as their nearest noble gas. Noble gases

have complete valence shells.

• An atom and an ion of the same element have

completely different properties, such as size.

• For example the Na atom is larger than the Na+ ion.

Compounds, Atoms, and Ions7.1

VOCABULARY

bond

valence shell

valence electron

ion

Chemical Bonding7.2

VOCABULARY

chemical bonds

ionic compounds

ionic bonding

covalent

molecular compounds

covalent bonding

molecule

diatomic molecules

phases

states

• A chemical bond is a force that holds atoms together to form compounds.

• There are two general types of bonds: ionic and covalent.

• Ionic bonds involve a transfer of electrons between atoms. Ionic bonding forms ionic compounds.

• For example CaF2

• Covalent bonds involve a sharing of electrons between atoms. The basic unit of a covalently bonded compound is a molecule. Covalent bonds form molecular compounds.

• For example O2

Chemical Bonding7.2

VOCABULARY

chemical bonds

ionic compounds

ionic bonding

covalent

molecular compounds

covalent bonding

molecule

diatomic molecules

phases

states

• Ionic compounds separate into ions when

dissolved in water and can conduct electricity,

while covalent compounds do not separate into

ions, nor do they conduct electricity.

Ionic Compounds: Chemical Formulas and Naming7.3

VOCABULARY

chemical formula

ion charge balance

multivalent

polyatomic ions

• A chemical formula describes the proportions of the component elements.

• The chemical formulas for ionic compounds can be predicted by balancing ion charges.

• The fundamental rule for determining the chemical formula for any ionic compound is that the total ion charge for the compound is zero.

• The chemical names are derived from the ion names.

• For example: NaCl = sodium chlorideK2O = potassium oxide

• Ionic compounds can be divided into three types:• binary ionic compounds• ionic compounds with multivalent elements• ionic compounds with polyatomic ions

Molecular Compounds: Chemical Formulas and Naming7.4

• Molecular compounds result when atoms of non-metals share

electrons to bond.

• The chemical formulas for molecular compounds are derived from

their chemical names (and vice versa) based on a prefix system.

• Charge balancing is not required for molecular compounds.