Putting Atoms Together

Learning Goal for Today

• Understand how chemical formulas are used to represent compounds

• Learn characteristics of ionic and molecular compounds.

Atoms and Molecules

Atoms

2 or more chemically

joined

Molecules

Elements and Compounds

Elements

2 or more chemically joined

Compounds

Terminology… Recall:

• A molecule consists of two or more atoms that are chemically joined together.

• A chemical formula indicates the type and number of atoms in a molecule.

• Note: the coefficient in front of the formula multiplies the number of atoms of each element in the formula.– Example:

• 2CO2 means 2 carbon and 4 oxygen atoms

Types of Molecules (Overview)

1. Molecular Element: Two non-metal atoms of the same element A.k.a. “diatomic molecules”

H2 , N2 , O2 , F2 , Cl2 , Br2 , I2

Types of Molecules

2. Molecular Compounds: Formed with ≥2 different

non-metalsHeld with covalent

bondsExamples:

• CO2 carbon dioxide

• H2O water

3. Ionic Compounds:positively and negatively

charged ionsCommonly formed from

metals and non-metalsHeld with ionic bondsExamples:

• NaCl sodium chloride

• MgCl2 magnesium chloride

Try This

• Handout: “Chemical Formula”

Ionic Bonding

Ion:• a particle that has either a positive or negative

charge• “forms when an atom loses or gains one or

more electrons without changing its number of protons”

• Examples:– Mg loses two electrons Mg2+

– Br gains one electron Br-

Ionic Bonding

Cation:• a positively charged

ion• forms when an atom

loses one or more electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge

• Example:– Na+

Na

11 p+

12n0

Ionic Bonding

Cation:• a positively charged ion• forms when an atom loses one or more

electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge

• Example:– Na loses one e-

Na

11 p+

12n0

Ionic Bonding

Cation:• a positively charged ion• forms when an atom loses one or more

electrons, leaving more protons (+) than electrons (-) and resulting in a net positive charge

• Example:– Na loses one e- Na+

Na+

11 p+

12n0

Ionic Bonding

Anion:• a negatively charged ion• forms when an atom gains one or more

electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge

• Example:– Cl

Cl

17 p+

18 n0

Ionic Bonding

Anion:• a negatively charged ion• forms when an atom gains one or more

electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge

• Example:– Cl gains one e-

Cl

17 p+

18 n0

Ionic Bonding

Anion:• a negatively charged ion• forms when an atom gains one or more

electrons, leaving more electrons (-) than protons (+) and resulting in a net negative charge

• Example:– Cl gains one e- Cl-

Cl-

17 p+

18 n0

Ionic Bonding

Ionic Bond:• a bond formed when a metal and a non-metal

transfer electrons• held together by the attraction between the

positively charged metal (cation) and the negatively charged non-metal (anion)

• Example:– NaCl [Na]+[Cl]-

Ionic Bonding

Na

11 p+

12 n0

Cl

17p+

18n0

Ionic Bonding

Na

11 p+

12 n0

Cl

17p+

18n0

Ionic Bonding

Na+

11 p+

12 n0

Cl-

17p+

18n0

Naming Ionic Compounds

1. Name the metal2. Name the non-metal3. Add “ide” to the non-metal

Name of Metal Name of non-metal + ideSodium chloride

How do we find the formula?

• Li1+ and O2-

• What do you notice?

• 2 Lithium atoms• 1 Oxygen atom• Li2O

Here’s the trick

1. Write the symbols and charges

2. Crisscross

3. Write symbols with subscripts

Li 1+ O 2-

Li 1+ O 2-

Li2O1

Li2O

Try This!

• “Ions and Ionic Bonding” worksheet

Molecular (Covalent) Bonding

Covalent Bond:• formed when two non-metal atoms share electrons

Covalent Bonding

• Very strong bond; requires a lot of energy to form/break

• Example:– H2 H—H

Covalent Bonding

1 p+

H

1 p+

H

Covalent Bonding

1 p+

H

1 p+

H

Covalent Bonding

1 p+ 1 p+

H—H

Prefixes for Naming Molecular Compounds

# atoms Prefix1 Mono2 Di3 Tri4 Tetra5 Penta6 Hexa

Never use “Mono” for the first element!

Ex. CO2

x Monocarbon dioxide

Carbon dioxide

Formula Name

1. Write the name of each element

2. Write the subscripts as prefixes

3. Change ending of last element to “ide”

Ex. H2O1

1. Hydrogen oxygen

2. Dihydrogen monoxygen

3. Dihydrogen monoxide

Now you try

CCl4

How did you do?

CCl4

1. Carbon chlorine

2. Carbon tetrachlorine

3. Carbon tetrachloride

Name Formula

Dihydrogen Dioxide

1. H O

2. H2O2

1. Write the names as symbols

2. Write the prefixes as subscripts

Now you try

• Dinitrogen Tetroxide

How did you do?

Dinitrogen Tetroxide

1. N O

2. N2O4