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39 terms

LC Chem 2.1 Chemical Bonding

chemistry
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Compound
A substance that is made up of two or more different elements combined together chemically.
Octet Rule
States that when bonding occurs, atoms tend to reach an electron arrangement with eight electrons in the outermost shell.
Exceptions to the octet rule
1. Transition metals can have more or less than eight electrons in their outermost energy level.
2. The elements near helium in the Periodic Table tend to achieve the electronic arrangement of helium with two electrons in the outer shell rather than eight.
Ion
A charged atom or group of atoms.
Cations
Another name for positive ions
Anions
Another name for negative ions
Ionic bond
The force of electrostatic attraction between oppositely charged ions in a compound.
Ionic substances
1. Contains a network of ions in the crystal.
2. Usually hard and brittle.
3. Have high melting points and boiling points.
4. Usually solid at room temperature.
5. Conduct electricity in molten state or when dissolved in water
Crystal lattice
The three dimensional structural arrangement of ions
Chemical formula
A way of representing a compound using symbols for the atoms present and numbers to show how many atoms of each element are present
ide
Ending for compounds which contain just two elements
ate
Ending for compounds which contain oxygen as well as the other two elements
Transition metal
An element that forms at least one ion with a partially filled d sublevel
Molecule
A group of atoms joined together. It is the smallest particle of an element or compound that can exist independently.
Valency
The number of atoms of hydrogen or any other monovalent element with which each atom of the element combines
Covalent bond
The chemical bond formed by sharing a pair of electrons
Single bond
Formed when one pair of electrons is shared
Double bond
Formed when two pairs of electrons are shared
Triple bond
Formed when three pairs of electrons are shared
Sigma bond
Formed by the head on overlap of the two atomic orbitals (s or p)
Pi bond
Formed by the sideways overlap of two p orbitals
Covalent substances
1. Contains individual molecules.
2. Usually soft.
3. Have low melting and boiling points.
4. Usually liquids, gases or soft solids at room temperatures.
5. Do not conduct electricity
Electronegativity
The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond.
Pauling
Scientist who studied the amounts of energy needed to break certain bonds and so set up a scale of relative values of electronegativity.
Non-polar covalent
Bond where the electrons are equally shared. Electronegativity difference less than 0.4
Polar covalent
Bond where the electrons are not equally shared. Electronegativity difference between 0.4 and 1.7 inclusive
Ionic
Bond with an electronegativity difference greater than 1.7
Intramolecular
Types of bonds hold atoms or ions together within the molecule or crystal lattice.
Intermolecular
Types of bonds that exist between one molecule and another.
Van der Waals forces
Weak attractive forces between molecules resulting from the formation of temporary dipoles. (The only forces of attraction that exist between non polar molecules. Their strength increases as the molecules get bigger due to the greater number of electrons in the electron clouds allowing the temporary dipoles to form more easily.)
Dipole dipole forces
Forces of attraction between the negative pole of one molecule and the positive pole of another. (Give rise to higher boiling points than those of similar non polar molecules.)
Hydrogen bonds
Particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. (The hydrogen atom acts as a bridge between two electronegative atoms. The boiling points of H2O, HF and NH3 are much higher than other hydrogen compounds.)
N O and F
Elements which will undergo hydrogen bonding with hydrogen
VSEPR Theory
Valence Shell Electron Pair Repulsion Theory - used to determine the shapes of molecules
Linear
2 bond pairs. Bond angle = 180°
Triangular planar
3 bond pairs. Bond angle = 120°
Tetrahedral
4 bond pairs. Bond angle = 109.5°
Pyramidal
3 bond pairs and 1 lone pair. Bond angle = 107°
V-shaped
2 bond pairs and 2 lone pairs. Bond angle = 104.5°