Chemical Compounds
Compounds are formed when atoms come close enough that their electron shells and nuclei interact. Compounds are formed
when chemical bonds are formed.
A compound has a chemical formula. A given compound is always made of the same elements in the same proportion.
Chemical structure shows the bonding within a compound
Bond length gives distance between the nuclei of two bonded atoms
Bond angles tell how these atoms are arranged in space, CO, H2O, NH3, CH4
Types of Compounds – Ionic, Covalent (aka Molecular) and Metallic
Ionic compounds, form when positive ions (Cations) bond to negative ions (Anions).
These are also called Salts. These compounds are solid, strong, and have high melting points.
Metals become positive ions called cations when they lose electrons. Metals can lose one to seven electrons.
Li
The nonmetals become negative ions called anions when they accept the electrons from the metals.
F
The positive cations are attracted to the negative anions, so ionic compounds are formed.
Examples: Na+ and Cl- form Na-Cl.
Ionic compound = Metal – Nonmetal
Covalent (or molecular) compounds, form when Nonmetals bond together.
These atoms share the electrons. No ions are formed. There is no loss or gain of electrons.
These compounds can be solid, liquid or gas, solids are softer and have lower melting points.
They do not conduct electricity. Examples: CO, CF4. Covalent compound = Nonmetal --Nonmetal
CO Carbon monoxide
CO2 Carbon dioxide
BCl3 Boron trichloride
CCl4 Carbon tetrachloride
PO5 Phosphorous pentoxide
SF6 Sulfur hexafluoride
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Bonds – Ionic, Metallic and Covalent
Atoms are held together via bonds. Bonded atoms usually have a stable electron configuration because the outer layer has
reached the octet.
Bonds can bend and stretch without breaking
H2O
Ionic Bonds are formed between oppositely charged ions
Ionic bonds are formed when one atom has donated electrons and the other has gained electrons.
Ionic compounds are in the form of solid networks, not single molecules
formula unit, NaCl, MgO,
When melted or dissolved in water, ionic compounds conduct electricity:
Solid ionic compounds do not conduct electricity because ions are locked into place.
Liquid ionic compounds conduct electricity because ions are free to move
NaCl in water;
Metallic Bonds
Electrons move freely between atoms. metal-metal bonds formed by the attraction between positive nuclei of the metals and the
electrons around them. The electrons free to move from atom to atom (Copper is the best metal to conduct electricity).
Covalent Bonds Atoms joined by covalent bonds share electrons. There is no transferring of electrons because both need to gain
electron(s). The electron shared are the valence electrons.
Covalent bonds can be Nonpolar or polar.

nonpolar covalent bonds-sharing equally, F-F, Cl-Cl, O-O, N-N
Atoms may share more than one pair of electrons

double bonds- two pairs of electrons is shared (total 4) O=O

triple bonds- three pairs of electrons shared (total 6) N≡N

triple bonds stronger than double bonds. It requires more energy to break triple bonds
Atoms do not always share electrons equally

polar covalent bonds- not sharing equally (unequal sharing). Depends on electronegativity- The ability of an element to
attract electrons to itself.

elements that are located to the further top right of periodic table attract electrons the most, Fluorine is the element that
attracts the electrons the most. Fluorine has the highest electronegativity. Francium the least.
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C-Cl4, N-O
Polyatomic Ions Covalently bonded atoms that exist as cluster of atoms. There are many common polyatomic ions. Parentheses
group the atoms of a polyatomic ion
Ammonium, (NH4)+
Carbonate, (CO3)2Hydrogen carbonate, (HCO3)-1
Nitrate, (NO3)Nitrite, (NO2)Sulfate, (SO4)2Sulfite, (SO3)2Phosphate, (PO4)3Phosphite, (PO3)3example: ammonium sulfate, (NH4)2SO4,
parentheses are to remind you that the atoms of a polyatomic ion act as a single ion
Ionic compounds with transition metals
Determining the charge of a transition metal cation
The ionic compounds have a total charge of zero. The total positive charges must equal the total negative charges.
1.
Always start by setting Oxygen as minus 2, O-2.
2.
Multiply by the number of oxygen atoms present.
3.
Divide by the number of metal atoms present
TiO
Titanium (II) oxide
TiO2
Titanium (IV) oxide
FeO
Iron (II) oxide
Fe2O3
Iron (III) oxide
Find the charge and Name the following, Use Handout on naming compounds.
CrO,
Mn3O4
Mn2O3,
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18 Groups
1
7 Periods
2
3
4
5
6
7
The periodic table is arranged in order of increasing atomic number. This number is shown above the symbol
of the element. The atomic number is the number of the positive subatomic particles called protons. Because the atoms
are neutral the number of electrons is the same as the number of the protons. The atomic mass is written under the
symbol of the elements
The number of the neutrons can be determined by using the atomic mass. This number is the sum of the mass
of the protons and the mass of the neutrons. Rounding the atomic mass to a whole number gives the mass number.
Number of neutrons = Mass number – number of protons. For Beryllium # Neutrons = 9 – 4 = 5
There are 18 vertical groups and 7 periods in the periodic table. The bold staircase line separates the metals
from the nonmetals. To the left of the staircase line are the metals. These are the majority of the elements. To the right
of the staircase line are the nonmetals.
The number of the period is useful when drawing the Bohr model of the atom. An element in the second
period is drawn with two circles around the nucleus. To determine the number of electrons that are to be used in the
Bohr model count the boxes including the one containing the element involved. Remember that the orbitals (the circles)
are filled in the following order; 2, 8, 8.
Elements in the same group have the same number of valence electrons and for this reason have similar
properties.
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