Unit 1(b) - Periodicity Flashcards
What is a periodic pattern?
A pattern which repeats across a period in the periodic table
What did Mendeleev use to arrange the then known elements?
Increasing masses and similar chemical properties
How is the modern periodic table arranged?
Increasing atomic number
In the modern periodic table, what are trends related to?
Bonding and structure
What is the covalent radius of an atom?
Half the distance between the nuclei of two bonded atoms of the element
What happens to atomic size as you move across a period?
Atomic size decreases, as the increasing nuclear charge pulls electrons closer to the nucleus
What happens to atomic size as you move down a group?
Atomic size increases as an extra electron shell is added, as well as nuclear attraction decreasing due to shielding by inner electrons
What is the density of a substance?
It’s mass per unit volume
What happens to density as you move across a period?
The general trend is that in any period, density first increases from group 1 to a maximum in the centre, then decreases again towards group 0
What happens to density as you move down a group?
Density increases as the mass of the atom is increasing faster than the volume
What do melting and boiling points indicate?
The strength of the forces between particles
What happens to mps and bps as you move across a period?
Increase from group 1 to group 4 (group 4 elements are covalent networks), then decrease to group 0
What happens to mps and bps as you move down group 1?
Melting and boiling points decrease as there is a decrease in attraction between atoms
What happens to mps and bps as you move down group 7
Melting and boiling points increase as LDF attractions between molecules increase
What is the first ionisation energy?
The energy required to remove one mole of electrons from one mole of gaseous atoms
What are the second (and subsequent) ionisation energies?
The energies required to remove further moles of electrons
What happens to ionisation energy as you move across a period?
Ionisation energies increase as the increasing nuclear charge pulls electrons closer to the nucleus
What happens to ionisation energy as you move down a group?
Ionisation energy decreases as the outer electrons are further from the nucleus, and the shielding effect from the inner electrons reduces the nuclear attraction for outer electrons
What is electronegativity?
A measure of the attraction an atom in a bond has for the electrons of the bond
Which element is the most electronegative?
Fluorine
What happens to electronegativity as you move across a period?
Electronegativity increases as the nuclear charge increases, attracting the electrons more strongly to the nucleus
What happens to electronegativity as you move down a group?
Electronegativity decreases because the number of electron shells increases. This means electrons are further from the nucleus and the shielding effect of inner electrons increases
What are the properties and structure of elements related to?
The types of bonding present
What is a metallic bond?
Electrostatic attraction between positive nuclei and delocalised outer electrons
What do metallic structures consist of?
A giant lattice
What is metallic bond strength?
A measure of the no. of outer electrons. The greater the no. of electrons, the stronger the metallic bond
What are some characteristics of metals?
- Shiny
- Malleable
- Ductile
- Good electrical and heat conductors
What happens to metallic character as you move across a period?
It decreases as the mobility of the electrons as they are restricted by the increasing nuclear charge
What happens to metallic character as you move down a group?
It increases as outer electrons are held more loosely due to shielding
What is the relationship between metallic bond strength and metallic character?
The stronger the metallic bond, the less the metallic character
How does the size of metal atoms relate to melting and boiling points?
Smaller metallic atoms have larger melting and boiling points
What are metal boiling points dependant on?
- How many electrons are in the outer shell
* No. of electron shells
Why are the noble gases stable?
They have full outer electron shells, meaning they are chemically stable and monatomic
Why do noble gases form liquids and solids at low temperatures, despite being monatomic?
Weak intermolecular forces - LDF
What is LDF?
The attraction between the temporary dipoles caused by uneven distribution of moving electrons
What is a dipole
An unequal distribution of charge
What is a covalent bond?
The electrostatic attraction between the positive nuclei and the negative shared electrons
What kinds of bonding are present in diatomic molecules?
Strong intramolecular bonding (covalent) and weak intermolecular bonding (LDF)
Give examples of discrete covalent molecular solids
Phosphorous (P4), sulphur (S8), and carbon (fullerenes)
Why are phosphorous and sulphur solids at room temperature, whereas chlorine is a gas?
P and S are larger with more atoms, so have more opportunities for LDF. Chlorine forms diatomic molecules which are gaseous at room temperature
What is a covalent network?
A covalent network structure consists of a giant lattice of covalent lay bonded atoms
What is the structure of boron?
Boron forms B12 groups which are inter bonded with each other, resulting in an element almost as hard as diamond. It has a very high melting point
What two network forms does carbon exist as?
Graphite and diamond
What are some properties of graphite?
- Layers of atoms in hexagonal plates
- 3/4 outer electrons covalently bonded, 4th outer electron moves within layer
- Conducts electricity due to delocalised electron
- Soft, slippery, used as a lubricant
What are some properties of diamond?
- Regular tetrahedral structure
- All 4 outer electrons covalently bonded
- Does not conduct electricity
- Hardest natural substance, used in cutting tools
What element is similar in structure to carbon?
Silicon
