View
215
Download
2
Category
Preview:
Citation preview
The Elements
• 90 naturally occurring elements• Most are not found as pure elements• The majority of elements are found combined
with other elements to form compounds. • Gold, silver and platinum are rare examples of
metals found in elemental form (precious metals)
Classifying
• Since the 90 elements can form thousands of different compounds, classification systems have been developed.
• The classification of compounds is based on their properties to help our understanding of compounds.
• Example: melting point, boiling point, hardness, etc.
Electron Configuration
a) Atomic number = number of electrons
b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.
c) Electron configuration determines how an atom behaves when it encounters other atoms
Electron Dot Structure
Symbols of atoms with dots to represent the valence-shell electrons
1 2 13 14 15 16 17 18H He: Li Be B C N O : F :Ne :
Na Mg Al Si P S :Cl :Ar :
Chemical Bonds
Octet Rule- rule that states that atoms tend to gain, lose, or share electrons so that each atom has full outermost energy level which is typically 8 electrons.
There are two ways to try to do this1. Ionic bonds – 2. Covalent bonds –
Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to N would like toO would like to
Gain 4 electronsGain 3 electronsGain 2 electrons
Chemical Bonds
• forces that attract atoms to each other to form compounds
• involves the interactions of valence electrons between atoms
• usually the bond forms a compound that is more stable than the atoms individually.
Formation of Ions from Metals
Ionic compounds result when metals react with nonmetals
Metals lose electrons to match the number of valence electrons of their nearest noble gas
Positive ions (cations) form when the number of electrons are less than the number of protons
Group 1 metals ion 1+
Group 2 metals ion 2+
• Group 13 metals ion 3+
Formation of Sodium Ion
Sodium atom Sodium ion
Na – e Na +
2-8-1 2-8 ( = Ne)
11 p+ 11 p+
11 e- 10 e-
0 1+
Ions from Nonmetal Ions
In ionic compounds, nonmetals in 15, 16, and
17 gain electrons from metals (anions)
Nonmetal add electrons to achieve the octet
arrangement
Nonmetal ionic charge:
3-, 2-, or 1-
Fluoride Ion
unpaired electron octet 1 -
: F + e -> : F :
2-7 2-8 (= Ne)
9 p+ 9 p+
9 e- 10 e- 0 1 -
ionic charge
Ionic Bond
• Between atoms of metals and nonmetals (usually) with very different electronegativity
• Electronegativity difference e.d. > 1.7• Bond formed by transfer of electrons• Examples; NaCl, CaCl2, K2O
Some characteristics of an Ionic Bond
1. Crystalline at room temperatures2. Have higher melting points and boiling points
compared to covalent compounds 3. Conduct electrical current in molten or
solution state but not in the solid state4. Polar bonds
Covalent Bond
• Between nonmetallic elements of similar electronegativity.
• Formed by sharing electron pairs
• Examples; O2, CO2, C2H6, H2O, SiC
Some characteristics of a Covalent Bond
1. Covalent bonds have definite and predicable shapes.
2. Very strong3. Low melting and boiling points
Covalent Bonds can have multiple bonds, so you should be familiar with the following…
• Single Covalent Bond- chemical bond resulting from sharing of an electron pair between two atoms.
Double Covalent Bond- chemical bond resulting from sharing of two electron pairs between two atoms.
Triple Covalent Bond-chemical bond resulting from sharing of three electron pairs between two atoms.
•water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.
Electronegativity (EN)
• a measure of an atoms ability to attract electrons in a chemical bond.
• a property of an atom involved in a bond
Using EN to predict the bond type
When two atoms form a bond the difference in electronegativity (ΔEN) can help to determine the bond type.
| | | 0 0.5 1.7 3.3
Recommended