Topic 3 - Covalent Substances Flashcards
Covalent Bonds
- covalent bonding is when non-metals share valence electrons to form molecules
- covalent bonds mostly happen for the non-metal elements
Octet Rule
More stable = 8 electrons
Intramolecular Bonds
bond within the molecule
Single covalent bonds
when atoms share two electrons, one from each atom, the covalent bond formed is called a single covalent bond, indicated by a straight line
Diatomic Molecules
- two elements of the same or different atoms
- can be hydrogen and Chlorine or oxygen oxygen and so on.
Lewis structures: electron dot diagram
show the valence shell electrons as they are involved in bonding
Non-Bonding Electrons
The outer-shell electrons that are not involved in bonding are called non-bonding electrons
Delocalised Electrons
Electrons are free to move
Lone Pairs
Pairs of non-bonding electrons are known as lone pairs
Double Covalent Bonds
Two pairs of electrons (four elements in total) are shared between the atoms, rather than just one pair.
Triple Covalent Bonds
A triple covalent bond occurs when three electron pairs are shared between two atoms
Molecular Compounds
- Diatomic molecules - contain two atoms they can be the same or different
- Polyatomic molecules contain more than two atoms
Why diamond is very hard
Carbon atoms in diamond are strongly covalently bonded throughout the structure, leading to a very hard substance.
Why diamond is a non-conductor of electricity
Each carbon in diamond bonds with four other carbon atoms, meaning that all electrons are localised in bonding and there are no freely moving charged particles.
diatomic molecules
molecules made up of 2 elements
Polyatomic Molecules
two single covalent bonds, each containing
a shared electron pair
- four non-bonding electrons on the oxygen
atom.
Shape of Molecules affect…
Molecular shape affects melting point, boiling point, hardness
and solubility.
Structural Formula
with lines and no electrons shown
What is Electronegativity
Electronegativity is the ability of an atom to attract electrons towards
itself when forming a chemical bond.
Non-Polar
Bonds with an equal distribution of bonding electrons
electrons shared equally
symmetrical
Polar
Bonds with an imbalanced electron distribution
not shared equally
asymmetrical
Pyramidal and Bent are
Asymmetrical
Intramolecular bonds
Covalent bonding
Between Element
stronger
Intermolecular bonds
Weaker
joining different covalent bond together
The strength of intermolecular forces is determined….
by the size, shape and polarity of molecules.
Intermolecular Forces
dispersion forces: polar and nonpolar molecules, caused by temporary dipoles
dipole–dipole attraction: polar molecules only
hydrogen bonding
Dispersion Forces
The molecular mass increases, the dispersion forces become stronger
Molecules that form long chain will tend have stronger dispersion forces.
The stronger the dispersion forces of a substance, the higher its boiling point.
all polar and non polar
Dipole Dipole Attraction
- can only occur in polar molecules
- the more polar a molecule is, the stronger the dipole-dipole attraction
Hydrogen bonding only occurs with
Nitrogen, Oxygen, Flourine
Hydrogen Bonding
Hydrogen bond is approximately ten times stronger than a dipole–dipole attraction,
but about one-tenth the strength of an ionic or a covalent bond.
Allotropes
Some elements can exist with their atoms in several different structural arrangements
called allotropes.
Allotropes of Carbon
- Diamond
Covalent Bonds, Dispersion Force
Tetrahedral, Network Lattice Structure
Very High melting point, does not conduct electricity, very hard and rigid, high thermal conductivity
drill tips
Allotropes of Carbon
- Graphite
Strong covalent bonds, weak dispersion force
covalent layer lattice
slippery and soft, resistance to heat, high electrical conductivity
Battery electrodes, lubricant
Allotropes of Carbon
- Amorphous Carbon
Surface interaction between fine carbon particles
no consistent structure
interaction between the fine carbon particles increases the strength and toughness of the product
flue, printer toner ink
Electronegativity
increase left to right and up a group
What elements dont follow the octet rule
hydrogen, beryllium, or boron
Why does diamond not melt but sublime (solid) - gas
Since the bonding in diamond is of equal strength throughout the lattice, if sufficient heat is supplied to break a covalent bond, all covalent bonds can be broken.
There is no weak bonding in diamonds.
