Elements and Compounds

(Unit Two, Lesson 2.6)By Margielene D. Judan

Lesson Outline:

Matter: An OverviewPure SubstanceElement vs. CompoundMetals, Metalloids, NonmetalsLaw of Definite Composition

Copy the table. This will help you distinguish classifications of matter.

PURE SUBSTANCE

A form of matter which cannot be separated by physical means.

It is further classified into two: ELEMENTS and COMPOUNDS.

ELEMENTS VS. COMPOUNDS

1. Contains only one kind of atom

1. Contains two or more kinds of atoms

He HH

O

Water (H2O)Helium Oxygen (O2)

O

O

ELEMENTS VS. COMPOUNDS

2. Cannot decompose by ordinary chemical means

2. Can decompose by chemical means.

He HH

O

Water (H2O)Helium atom

will not decompose

When water decomposes, they will separate from each other, forming 2 helium gas, and one oxygen gas. H

H

O

That is what you see when water boils: the oxygen and hydrogen steam.

Water decomposes into steam

ELEMENTS VS. COMPOUNDS(SUMMARY)

1. Contains only one kind of atom

2. Cannot decompose by ordinary chemical means

1. Contains two or more kinds of atoms

2. Can decompose by chemical means.

ELEMENTS VS. COMPOUNDS(EXAMPLES)

Oxygen (O2)

Helium (He) Nitrogen (N2)

Sodium (Na) Chlorine (Cl) and more (There are

currently 115 known elements)

Sodium chloride/salt (NaCl) Water (H2O)

Aluminum oxide (Al2O3)

Carbon dioxide (CO2)

Alcohol (C2H5OH)

Ammonia (NH3)

Silicon dioxide/ sand (SiO2)

etc. (There are millions of compounds)

ELEMENTS VS. COMPOUNDS(CLASSIFICATION)

1. Metals

2. Metalloids

3. Nonmetals

1. Acids

2. Bases

3. Salts

ELEMENTS

Metal – conducts heat and electricity (conductor)

Metalloid – exhibits both properties of metal and non-metal (conductor and insulator)

Nonmetal – doesn’t conduct heat and electricity (insulator)

Look at your periodic table. Did you see a ladder-shaped line or pattern?

The elements adjacent to it (colored blue) are the metalloids

There are 7 metalloids:

1. Boron (B)

2. Silicon (Si)

3. Germanium (Ge)

4. Arsenic (As)

5. Antimony (Sb)

6. Tellurium (Te)

7. Polonium (Po)

*Antimony (At) is not a metalloid

Metals are all elements to the left of metalloids.

Nonmetals are those to the right of metalloids.

With your Periodic Table, classify whether they are metal, metalloid, or nonmetal.

1. Oxygen

2. Silicon

3. Calcium

4. Potassium

5. Lead

6. Boron

7. Neon

8. Iodine

9. Astatine

10.Gold

Answers:

1. Oxygen (nonmetal)

2. Silicon (metalloid)

3. Calcium (metal)

4. Potassium (metal)

5. Lead (metal)

6. Boron (metalloid)

7. Neon (nonmetal)

8. Iodine (nonmetal)

9. Astatine (nonmetal)

10.Gold (metal)

COMPOUNDS: Law of Definite Composition

A molecule of a compound has a definite number of atoms.

Examples:H2O – 2 molecules of H, 1 molecule of O

NH3 – 1 molecule of N, 3 molecules of H

Vinegar (CH3COOH) – 2 mol C, 4 mol H, 2 mol O

According to their electron configurations, elements are classified as s block elements p block elements d block elements f block elements

We will not study what these blocks mean (this is higher chemistry) but we’ll just use these blocks to classify our elements.

Short Quiz tomorrow: Memorize the abbreviations and the meanings of the elements in the s block.

Sources:

Science Links 7