U1 periodicity Flashcards
How are elements arranged on the periodic table?
In order of increasing atomic number
Groups:
-vertical columns
-contain elements if similar properties
-common number of electrons in outer shell
periods:
-rows of elements
-increasing atomic number
-increasing number of electrins
-move from metallic to non-metallic characteristics
What does the periodic table allow chemists to do?
make accurate predictions of physical properties and chemical behaviour for any element, based on its position
What is the atomic radius?
Distance from the centre of nucleus to outer electron shell
What is covalent radius?
half the distance between two nuclei in a bond. A measure of the size of an atom
What happens to atoms as you go down a group and why?
Get bigger:
-Greater number of electron shells
-Outer electrons not held as tightly by nucleus because they are further away
-Also due to more inner electrons, stronger shielding effect (electron repulsions)
What happens to atoms as you cross a period and why?
atoms get smaller:
-Bigger nucleus charge (more protons) holds outer electrons tighter
SAME NUMBER OF ELECTRON SHELLS
Working out which radius is bigger: covalent v ionic radius
Na 2,8,1 bigger radius
Na+ 2,8 smaller radius
Covalent radius is bigger as it has one more energy level
F 2,7 p=9+ e=9- smaller radius
F- 2,8 p=9+ e=10- bigger radius
Ionic radius is bigger as protons have more electrons to pull (more electrons need to be pulled by the same number of protons)
What is ionisation energy?
Energy required to remove one mole of electrons from one mole of atoms in the gaseus state
2nd ionisation energy?
energy required to remove one mole if electrons from one mole of 1+ ions in the gaseus state
Na- Why is the 2nd ionisation energy much bigger than the 1st?
Because it’s removing an electron from a STABLE OUTER SHELL
More strongly attracted to the nucleus
What happens to the 1st ionisation energy as you descend a group?
gets smaller (electrons are easier to move)
Outermost electron is further from the nucleus (larger radius) and not held as tightly
Shielding/screening effect from inner electrons
-more shielded from nuclear pull
-less strongly attracted by nucleus
What happens to the 1st ionisation energy as you cross a period?
gets bigger (electrons are more difficult to remove)
Outermost electrons are held more tightly by increasing nuclear charge (more protons)
-less shielded from nuclear pull
-more strongly attracted by nucleus
Is removing an electron endo or exo
endo -
energy is needed
What is electronegativity?
A measure of the attraction an atom involved in a bond has for the electrons of the bond
What happens to electronegativity as you go to down a group?
Decreases (less pull on bonding electron)
Because the screening effect due to inner shell electrons means there is less attraction between the nucleus and the bonding electrons (atom gets bigger)
What happens to electronegativity as you cross a period?
Increases
Covalent radius decreases, nucleus charge increases so greater attraction for bonding electrons
Metallic elements
Li Be Na Mg Al K Ca
Monatomic elements
He Ne Ar
covalent molecular elements
C (half) N O F P S Cl
Covalent network elements
B C(half) Si
Metallic bonding: definition and properties
Strong electrostatic force of attraction between the - delocalised electrons and the + ions
In general, high mp+bp
(alkali metals are lower)
Conductors of electricity due to delocalised electrons
more outer electrons=more delocalised electrons=stronger metallic bonds=higher mp+bp
What are monatomic elements?
-exist ad single atoms
-noble gases exist as monatomic elements
-contain no intramolecular forces
Intra molecular forces
STRONG
hold atoms together in a chemical
Intermolecular forces
weak
Exist between atoms/compounds (van der waals forces)
LDFs
London dispersion forces (type if van der walls intermolecular force)
-Forces of attraction that can operate between all atoms and molecules
-Formed as a result if electrostatic attractions between temporary dipoles and induced dipoles caused by the movement/uneven distribution of electrons in atoms and molecules
-The strength of LDFs is related to the number of electrons within an atom or molecule
-weakest of the intermolecular forces
-attraction between temporary dipoles/induced dipoles
-caused by the wobble (imbalance of the position) of electrons
Why does the boiling point increase going down the noble gases?
Because going down the group the number of electrons in the atom increases so that the size of the dipole increases so greater attraction between atoms
List of covalent molecules
Diatomic-H2 N2 F2 O2 Cl2
Polyatomic-P4 S8
Fullerenes-C60 (buckyballs)
Mp+bp S8>P4>Cl2
More atoms=more/stronger LDFs=higher mp+bp
C60
Fullerenes
Buckyballs
Covalent molecules with higher mp+bp due to the large number of atoms—>stringer/more LDFs
Examples of Covalent Networks
ELEMENTS
B, C(diamond,graphite), Si can be categorised as covent networks
COMPOUNDS
silicon dioxide
silicon carbide
Ionic compounds
Electrostatic force of attraction between positive and negative ions
Ionic formulae can be written giving the simplest ratio if each type if ion in the substance
Ionic compounds form lattice structures of oppositely charged ions
Covalent bonding
Atoms share pairs of electrons
The covalent bond is a result of two positive nuclei being held together by their common attraction first the shared pair of electrons
What are polar covalent bonds formed?
When the attraction if the atoms for the pair of bonding is different (due to different electronegativity values between 2 atoms)
Delta positive and delta negative notation can be used to indicate the partial charges on atoms, which give rise to a dipole
Bonding continuum
Pure covalent bonding->polar covalent bonding->ionic bonding
Ionic character
The difference in electronegativities between bonded atoms fives an indicatkon kf the ionic character..
If the difference is large then the movement if bonding electrons from the element of lower electronegativity to the element if higher electronegativity is complete, resulting in the formation of ions
The higher the difference in EN—>the more polar—>the more ionic
What happens as you go down the halogen group? (from F to I)
Atoms get bigger (more electron shells, more electrons)—>LDFs will be stronger—>mp+bp will increase
When is a polar molecule described as polar?
When it has a permanent dipole (due to the difference of electronegativity between atoms)
The spatial arrangement (symmetry) of polar covalent bonds can result in a molecule being non-polar
-There must be a difference in electronegativity
-It is not symmetrical
Symmetrical atoms and molecules
-diatomic elements (non-polar anyways)
-hydrocarbons )alkenes, alkanes, alkynes)
-CO2
-A central carbon attached to the same 4 atoms
DRAW IT FLAST FIRST
What is the intermolecular force between molecules with a permanent dipole called?
permanent dipole-permanent dipole (polar-polar) attraction/interactions
How to test polarity?
Polar/non-polar substances in a burette and into a beaker
Charged balloon or rod
Stream of polar substance will bend
Hydrogen bonds
strongest intermolecular forces
strongest pd-pds due to the higher different in ENs (highly polar)
N, F, O have the highest ENs so form H2 bonds
Weaker than a covalent bond
Why are carboxylic acids and alcohols very polar?
presence of H bond
What is a solvent?
A liquid that substances dissolve in?
Can be polar or non-polar
What are immiscible liquids?
Liquids that don’t mix eg water and oil
Are non-polar liquids miscible or immiscible?
miscible
1-What type of solvent usually dissolves polar molecules?
2-What type of solvent usually dissolves non-polar molecules?
1-a polar solvent (eg water which is a polar molecule so a polar solvent)
2-a non/polar solvent
What is viscosity?
the ‘thickness’ of a liquid
What tests can we use to check viscosity?
-substance in burette—> the longer it takes to empty, the more viscous
-glass rod with lids on both ends. Turn upside down (air bubble forms)—> the longer it takes the bubble to reach the top, the more viscous
-measuring cylinder and drop ball bearing in—> longer it takes to drop to the bottom, the more viscous
What is volatility?
How easily something evaporates
2 factors that affect volatility
strength of intermolecular forces—>the stronger the forces, the less volatile
size of molecule—>the bigger the molecule, the less volatile
Why does ice float on water?
H bonding between molecules in ice results in an expanded structure that causes the density of ice to be less than that of water at low temperatures.
