Element BondingPages 541-542

• SCOS 4.02: Evaluate evidence that elements combine in many ways to produce compounds that account for all living and nonliving things

• Students will be able to…– describe a compound and molecule.– explain that all matter is made of compounds.

• Atoms combine with other atoms to form a chemical bond.

• As atoms combine, new substances are made.

• EXAMPLE: Na + Cl = NaCl or table salt

Molecules• A molecule is made of two or more atoms

joined by a chemical bond. • The atoms can be the same or different.

Is this a molecule?• YES (A)• NO (B)

Cl2

Is this a molecule?

• YES (A)• NO (B)

Is this a molecule?

• YES (A)• NO (B)

Methane (CH4)

Compounds

• A compound is made of two or more DIFFERENT elements chemically combined in a set ratio.

NaCl (table salt / sodium chloride)

Is this a compound?

• YES (A)• NO (B)

Carbon monoxide (CO)

Is this a compound?

• YES (A)• NO (B)

Nitrogen gas (N2)

Is this a compound?

• YES (A)• NO (B)

Ammonia (NH4)

Chemical Formula• A chemical formula represents a compound.• It shows the elements in the compound and

the ratio of atoms.

• EXAMPLE: H2O

• EXAMPLE: H2O2 (hydrogen peroxide)

Other Examples of Chemical Formulas

• CaCO3 (calcium carbonate) – found in chalk and shells of some animals

• C8H10N4O2 – caffeine

• HClO – bleach• MgSO4 – Epsom Salt

• NaHCO3 (sodium bicarbonate) – baking soda

What elements are inbaking soda (NaHCO3)?

A) hydrogen, oxygenB) soda, bakingC) sodium, hydrogen, carbon, oxygenD) nitrogen, aluminum, hydrogen, carbon,

oxygen

How many oxygen atoms are there in C2H4O2 (acetic acid or vinegar)?

A) 1B) 2C) 3D) 4

How many total atoms are there in C2H4O2 (acetic acid or vinegar)?

• A) 2• B) 4• C) 6• D) 8

How many sulfur atoms are in copper sulfate (CuSO4)?

A) 1B) 2C) 3D) 4

How many different elements are in potassium dichromate (K2CrO7)

A) 1B) 3C) 7D)9E) 10

How many hydrogen atoms are in ethanol: CH3CH2OH ?

A) 1B) 2C) 3D)6

How many different elements are in ethanol CH3CH2OH ?

A) 1B) 2C) 3D)4

How many total atoms are in ethanol CH3CH2OH ?

A) 2B) 4C) 7D)9

• Compounds have properties that are different from those of the uncombined elements.

Sulfur Silver Ag2S

• EXAMPLE: Sulfur and Silver combine to form Ag2S (silver sulfide), which is tarnish and black in color.

• EXAMPLE: Table sugar C12H22O11.

Hydrogen and Oxygen are both colorless gasses.

Carbon

Sugar

How do the elements bond?

• RECALL: Electrons orbit around the outside of an atom.

• Atoms tend to GIVE UP or ACCEPT electrons to create chemical bonds.

• Chemical bonds form when all atoms have filled their outer electron orbital.

• Sodium GIVES UP an electron and Chlorine ACCEPTS an electron.

• Sodium = 1+• Chlorine = 1-

Hydrogen GIVES UP an electron and Oxygen ACCEPTS two electrons.

Hydrogen = 1+Oxygen = 2-

Note: The compound must be neutrally charged. 1+1-2 = 0