Unit C: Atoms, elements, and Compounds
Chapter 7: Chemical compounds
Key Question:
Hoe do we handle environmental problems when things corrode or do not decompose?
Key Concepts:
1. Elements can combine to form compounds.
2. Metals and non-metals combine to form ionic compounds. Non-metals combine to
form molecules.
3. Some useful compounds have social, environmental, and economic impacts.
4. Compounds can break apart into simpler substances.
5. Molecular models are used to represent molecules.
6. Simple chemical tests can identify common gases.
7.1: Putting Atoms Together
pg. 257
Key Concepts:
1. Elements can combine to form compounds.
2. Metals and non-metals combine to form ionic compounds. Non-metals combine to
form molecules.
5. Molecular models are used to represent molecules.
Molecule: two or more atoms of the same or different elements that are chemically joined
together in a unit.
Chemical formula: notation that indicates the type and number of atoms in a pure
substance.
- Everything is made up of matter, but not of individual atoms. Matter is usually made up
combinations of atoms bonded together.
- Atoms bonded together can form molecules and compounds.
- Chemical formulas are used to indicate the type and number of atoms in a pure
substance.
- Subscripts are used to identify the number of each atoms, which makes up the molecule
or compound.
Oxygen Gas O2, made up of two oxygen atoms
Nitrogen Gas N2, made up of two nitrogen atoms
Figure 1: a) nitrogen molecule consists or two nitrogen atoms joined together, b) An
oxygen molecule consists of two oxygen atoms joined together.
Molecular Elements
Molecular element: a molecule consisting of atoms of the same element.
- There are several molecular elements, consisting of two of the =same atoms bonded
together.
Hydrogen
H2
Nitrogen
N2
Oxygen
O2
Fluorine
F2
Chlorine
Cl2
Bromine
Br2
Iodine
I2
- These are commonly known as DIATOMIC molecules.
Molecular Compounds
Molecular compound: a molecule that consists of two or more different elements.
- Molecular compounds are compounds that contain two or more different types of atoms
bonded together.
- Examples:
Water
Glucose
H2 O
C6H12O6
Carbon dioxide
Sucrose
CO2
C12H22O11
Figure 2: Water, H2O, is an example of a molecular compound.
Figure 3: Molecules of sugar consist of atoms of carbon, hydrogen, and oxygen.
- In nature there are only certain combinations of atoms to be found:
- Different combinations of the same type of atoms
O2
oxygen gas
O3
ozone
- Different combinations of atoms of different types:
Hydrocarbons:
CH4 Methane
C2H6 Ethane
C3H8 Propane
C2H4O2 Vinegar
C9H8O4 Aspirin
Organic Molecules:
C2H6O Alcohol
Figure 4: Molecules made from different combinations of the same elements can have
widely different properties.
Ionic Compounds
Ion: a particle that has either a positive or a negative charge.
Cation: a positively charged ion.
Anion: a negatively charged ion.
- Molecules are not compounds, but are molecules made up of neutral atoms bonded
together. Compounds consist of charged atoms which can form bonds with each other.
- Ions are atoms which have either lost or gained 1 or more electrons.
- When an atoms loses an electron, it will become positively charge, it has more protons
then electrons. A cation is positively charged atom.
- When an atom gains an electron, it will become negatively charged, it will more
electrons then protons. An anion is a negatively charged atoms.
- Atoms from Families I and II, (metals) found on the left side of the periodic table, form
cations, because they will lose one or two electrons.
- Atoms from Family XVII, (non-metals) are found on the right side of the periodic table,
will form anions, because they will gain one electron.
Example:
Sodium (Na) has one valence electron it will give up. Sodium has 11
protons in its Nucleus, and 11 electrons in its Electron Energy Shells.
When it loses one, there are 11 protons and 10 electrons, Therefore there
is a charge imbalance, one more proton then electron, creating a cation,
Na1+ or Na +.
Chlorine (Cl) has seven valence electrons and it requires one more
electron to make a complete octet. Chlorine has 17 protons in its Nucleus
and 17 electrons in its Electron Energy Shells. When Chlorine gains one
electron, there are 17 protons and 18 electrons. Therefore there is a charge
imbalance, one more electron then protons, creating a anion, Cl1- or Cl-.
Table 1: Sodium and Chloride Ions
Positive charge (protons)
Negative charge(electrons)
Ionic charge
Sodium, Na+
+11
-10
+1
Chloride, Cl+17
-18
-1
Bohr-Rutherford diagrams can be used to support this type of bonding.
Figure 6: A sodium atom (left) loses the electron in its outermost orbit and becomes a
positively charged sodium ion. A chlorine atom (right) gains an electron in its outermost
orbit and becomes a negatively charged chloride ion.
Ionic Compound: a compound that consists of positively and negatively charged ions.
- NaCl is called an ionic compound because it is created when two oppositely charge
atoms are attracted to each other and forms a compound by bonding.
Evidence of Learning: Students can …
- understand that atoms joining together form molecules.
- distinguish between molecules of elements and compounds.
- determine the number of atoms in a molecule from the chemical formula.
- explain the difference between atoms and ions.
- explain the difference between cations and anions.
Check Your Learning:
Questions 1 – 11, pages 261
Summary:
- Atoms can join together with other atoms to form larger units called molecules.
- Molecules may contain atoms of different elements or atoms of the same element.
- Molecules that contain atoms of the same element are called molecular elements
- Molecules that contain atoms of different elements are molecular compounds.
- A chemical formula indicates the type and number of atoms in a pure substance.
- Some compounds consist of charged atoms called ions. These compounds are called
ionic compounds.