Bonding (CDS) Flashcards
Describe the structure and bonding of atoms in a metal/alloy
Metal atoms are arranged in a regular lattice of cations surrounded by a sea of delocalised electrons
What holds metal atoms in their fixed positions?
The metal is held together by the non-directional electrostatic attractions between the cations and the delocalised electrons
Why do metals have high melting points?
Due to strong electrostatic attractions in their structure between cations and delocalised electrons
Describe and explain the trend in melting points of metals as you go across a period
As you go across a period, the melting point of metals increases as the charge on the ions increase.
Describe and explain the trend in melting points of metals as you go down a group
Down a group, melting points decrease because the shielding and atomic radius increases, so electrostatic forces of attraction between nuclei and delocalised electrons in the lattice are weaker.
Why can metals conduct electricity?
Because they have delocalised electrons which are free to move and carry a charge
Why can metals conduct heat?
Because delocalised electrons can absorb the heat energy and turn it into kinetic energy and move it around the structure of the metal.
Why are metals malleable and ductile?
Due to the delocalised electrons, which can move as the lattice is distorted, maintaining the non-directional electrostatic attractions and therefore hold the metals shape.
How are ions formed?
Ions are formed when electrons are transferred between elements that have a large difference in electronegativity
What type of ions do metals form?
Positive
What type of ions do non metals form?
Negative
Describe the crystal structure of ionic compounds
A regular lattice of alternating cations and anions forms.
What holds ions together in an ionic lattice?
Strong electrostatic forces between the ions
Why do ionic compounds have high melting points?
Due to strong electrostatic attractions between positive and negative ions which require lots of energy to break.
Why are ionic compounds soluble in water?
Water is very polar and can disrupt the electrostatic forces between ions and cause them to dissociate.
Why are ionic compounds electrical insulators when solid?
Because ions are fixed in position, and they cannot carry a charge.
Why are ionic compounds electrical conductors when molten or dissolved?
Ions are free to move around and carry a charge
Why are ionic compounds brittle?
When hit, alternating arrangement of ions is disrupted, so they repel each other and the lattice breaks apart.
What is a covalent bond?
A pair of shared electrons with opposite spin
What type of elements do covalent bonds form between?
Elements with high electronegativity (non-metals)
What are the forces of attraction involved in covalent bonds?
Electrostatic forces of attraction between the shared pair of electrons and the nuclei
What are the two types of electron pair in covalently bonded molecules?
Bonding pairs and lone pairs
How are covalent bonds represented?
With a line
What is a dative covalent bond/co-ordinate bond?
A covalent bond in which both shared electrons are donated by the same atom
How are co-ordinate bonds represented?
With an arrow pointing to the atom that is receiving the two electrons
Order these pairs in order of least to most repulsion:
Lone Pair - Lone Pair
Bonding Pair - Bonding Pair
Lone Pair - Bonding Pair
Least: BP - BP
LP - BP
Most: LP - LP
Bond angles in a linear molecule
180
Bond angles in a bent molecule
104.5
Bond angles in a trigonal planar
120
Bond angles in a tetrahedral molecule
109.5
Bond angles in a trigonal pyramid
107
Bond angles in a trigonal bipyramid
120 and 90
Bond angles in a octahedral molecule
90
Bond angles in a square pyramid
90
Bond angles in a square planar
90
What is electronegativity?
A measure of the power of an atom to attract a bonding pair of electrons.
What are the three most electronegative elements?
Nitrogen, Oxygen, Fluorine
What are the three intermolecular forces from weakest to strongest
Van Der Waals
Permanent Dipole
Hydrogen bonding
How and why do Van Der Waals forces vary with the size/ Mr of molecules?
They get stronger as molecules get bigger as there are more electrons
How are Van der Waals forces induced?
An instantaneous dipole in one molecule induces a dipole in another molecule and this induces a force of attraction between them.
Which type of molecules ONLY have Van Der Waals forces?
Monatomic elements
Diatomic Elements
Large non-polar molecules
True or False: All atoms and molecules have Van der Waals forces
True
What are permanent dipole forces?
Electrostatic forces of attraction between the dipoles of two polar molecules
What effect do permanent dipole forces have on the properties of a molecule
Greater melting and boiling point than expected due to energy required to break the stronger permanent dipole forces.
What is hydrogen bonding?
A type of permanent dipole force that occurs when hydrogen is bonded to a Nitrogen, Fluorine or Oxygen
Why is hydrogen bonding so much stronger than other permanent dipole forces?
N, O and F are the most electronegative elements so they create a very strong dipole.
What effect does hydrogen bonding have on the properties of a molecule?
Much higher melting and boiling points than expected
Why is ice less dense than water?
The orientation of hydrogen bonds causes molecules to push farther apart when frozen, which lowers the density.
Describe the structure of Ice
Ice has a 3D hexagonal crystal structure
What happens to solid iodine when it reaches its melting point?
It sublimes
Why is iodines melting point so low?
Because it only has weak VdW forces which are easily broken.
Describe the structure and bonding of diamond
Diamond has a tetrahedral structure. Each C makes 4 bonds with other carbons and they have a bond angle of 109.5 between them
Why is diamond hard?
Diamond is really hard due to its structure and the strong C – C covalent bonds
Why does diamond have a high melting point?
It has a very high melting point due to the strong C – C bonds which require lots of energy to break
Why doesn’t diamond conduct electricity?
All electrons are in a covalent bond so there is none available to move and carry a charge
Why isn’t diamond soluble in water?
Insoluble due to strong C – C bond
Describe the structure and bonding of graphite
- Hexagonal arrangement.
- Each C makes 3 bonds with other carbons, leaving a fourth delocalised valence electron for every carbon.
- Weak VdW forces hold the layers of graphite together.
- Bond angles between C is 120
Why does graphite have a high melting point?
Strong C – C bond require lots of energy to break
Why is graphite a conductor of electricity?
Due to delocalised electrons that are free to move and carry charge.
Why is graphite soft?
Easily broken VdW forces hold the layers together, so they can easily slide over each other making it soft
Why isn’t graphite soluble in water?
It is insoluble due to strong C – C bonds
