periodicity Flashcards
how are elements arranged in the periodic table
in increasing atomic number
what happens when you go down a group in the table
vertical columns within the table contain elements with similar chemical properties resulting in a common number of electrons in the outer shell
what happens when you go across a period in the table
rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from mettalic to non-metallic characteristics
what happens to the atomic size {covalent radius} as you go across a period
it decreases due to the increasing positive nuclear charge and there is a greater attraction between the increasing n.o of protons and electrons
what happens to the covalent radius as you go down a group
increases as you go down a group due to the increasing number of electron shells and there is more shielding as each extra layer of electrons ‘shields’ the outer electrons from the positive nucleus ie. there’s less of an attraction
what is the ionisation energy
ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms.
what happens to the ionisation energy as you go across a period
the atomic size decreases as the nuclear charge increases therefore the force of attraction on the outer electrons is greater and more energy is needed to remove an electron
what happens to the ionisation energy as you go down a group
decreases because the n.o of electron shells increase and extra layer of electrons help shield the outer electrons from nuclear attraction. More shielding of the outer electron’s from attraction from the nucleus therefore the force of attraction on the outer electrons is less and less energy is needed to remove an electron.
what is electronegativity
electronegativity is a measure of attraction for electrons in a covalent bond
what happens to the electronegativity across a period
it increases as there is an increase in the positive nuclear charge across a period and this causes the atom to attract bonded electrons more strongly
what happens to the electronegativity as you go down a group
it decreases as you go down a group because an increase in electron shells increases the distance the bonded electron’s are from the nuclear charge resulting in more shielding therefore, the electrons are less strongly attracted to the atom and elec. decreases
what is metallic bonding
electrostatic force of attraction between positively charged ions and delocalised electrons
what elements are metallic
Li , Be , Na , Mg , Al , K , Ca ,
what is ionic bonding
electrostatic force of attraction between positive ions of one element{normally a metal} an the negative ions of another element { normally a non-metal]
what is a covalent bond
a covalent bond is the result of 2 positive nuclei being held together by there attraction for a shared pair of electrons
give examples of covalent molecular
H2, N2, O2 , F2 , Cl2 , P4 , S8 ,
what is a polar covalent bond
polar covalent bonds are formed between atoms with different electronegativities. polar covalent substances have atoms which are slightly negative and slightly positive. this leads to permanent dipoles
what is a non polar bond
non polar covalent bonds are formed between atoms with the same electronegativities.
how do you detect polar covalent structures
polar covalent liquids are attracted to charged rods eg. a stream of water is deflected by a charged rod .
what is the bonding continuum uses for
used to understand different types of bonding by observing variations in electronegativity between atoms
what does the bonding continuum show us
the difference in electronegativities between bonded atoms gives an indication of the ionic character. The larger the difference, the more polar the bond will be. If the difference is large, then the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete, resulting in the formation of ions
what happens to molecules with symmetrical arrangements
molecules that have symmetrical arrangement of polar bonds act as non-polar molecules. in these cases, the polar bonds cancel each other out. therefore they have non polar structures
`how do intermolecular forces occur
the occur between atoms and molecules they are weak
where do intramolecular forces occur
bonds inside the molecule
what are the 3 type of van der waals’ forces
london dispersion forces
permanent dipole-permanent dipole interactions
hydrogen bonds
properties of london dispersion forces
- these are the weakest of all the intermolecular forces and occur between all atoms and molecules .
- LDF are caused by the uneven distribution of electrons which are constantly moving in an atom. this forms a temporary dipole on an atom.
what is the definition for LDF
LDF are the electrostatic forces of attraction between temporary and induced dipoles caused by the movement of electrons
what happens when an atom has a temporary dipole and induced dipole
as the atoms has a temporary dipole it can induce a dipole in a nearby atom. this results in an attraction between the temp dipole and the induced dipole ie a LDF
what has the strength of LDF got to do with the electrons
The strength of the LDF forces is related to the n.o of electrons within and atom or a molecule therefore covalent substances with similar numbers of electrons will have similar strength if LDF forces
example of melt/boiling point in the noble gases group in regard to LDF
the no of electrons increases as you go down the noble gas group. this means the LDF forces are becoming stronger. Due to this more energy is required to overcome the increasing forces of attraction. as a result the melt/boiling point increase.
what is permanent dipole-permanent dipole interactions
pd-pd interactions are intermolecular forces of attraction between polar covalent molecules
- occur in molecules that have large differences in electronegativities.
- pd-pd interactions are stronger than LDF for molecules with similar number of electrons
what is hydrogen bonding
hydrogen bonding occurs between molecules where there is an atom of H bonded to an atom of a strongly electronegativity element such as N , O , F eg water
what is the strongest type of intermolecular force
hydrogen bonding is the strongest type of intermolecular force but note that it is still weaker than a covalent bond.
what do water , hydrogen fluoride and ammonia have in common
HF , H2O, NH3 , all have anomalous boiling points due tot the presence of hydrogen bonding.
how is ice dense
the density of solid ice is unusually lower than liquid water due to hydrogen bonding. solid ice adopts an open lattice structure with loads of spaces making it less dense than water.
where are the intramolecular forces
in polar covalent and non-polar covalent molecules [inside the mol]
what are the intermolecular forces
LDF , PD-PD interactions , Hydrogen bonds
what do monatomic structures consist of
they consist of discrete (individual) atoms held together by london dispersion forces
what do covalent molecular structures consist of
covalent molecular structures consist of discrete (individual) molecules held together by weak intermolecular van der waal forces.
- many elements have covalent structures
- eg hydrogen, nitrogen, oxygen , fluorine, phosphorus , sulfur and chlorine
give examples of covalent molecular compounds
ammonia water methane and carbon dioxide
what do covalent network structures consist of
covalent network structures consist of giant lattice of atoms covalently bonded to each other , elements such as boron, silicon and some forms of carbon
tell us about carbon atom
carbon is unique because
- each carbon atom in diamond is covalently bonded to 4 other carbon atoms in a covalent network structure. it is used for cutting and grinding tools because of its strength.
tell us about graphite covalent network
in graphite each carbon atom is covalently bonded to another 3 atoms in a network structure.
- this leaves one electron free from each carbon atom
- these delocalised electron can move throughout the graphite structure
uses
- electrical conductor - conducts electricity due to delocalised electrons
what is fullerenes - covalent molecular structure
are made up of large molecules containing between 60-80 carbon atoms
-they have covalent molecular structures with weak LDF between the molecules
why does -element 1- have a higher melting point than element 2
as can be seen from the formulae there are more atoms in (element 1 ) compared to a (element 2) molecule. both the elements have LDF however element 1 molecule has more electrons and as a direct result will have stronger LDF between the molecules. more energy will be required to overcome these stronger forces.this is hy element 1 has a higher melt point then element 2.
what do the melting and boiling point depend on
the melting and boiling point of a substance depends on the strength of the force or bond that has to be broken
- the melting and boiling points of polar substances are higher than the melting and boiling point of non-polar substances with similar numbers of electrons
do metals and ionic compounds have high or low melt-boil points
both metal and ionic compounds have high melt-boil points due to large lattice structures they have
do covalent network structures have high or low melting -boiling points
tend to have high melt-boil points due to strong covalent bonds have to be broken
noble gases melt boiling point
descending the noble gases results in an increase in the number of electrons which also results in an increase in the strength of the LDF. this means that the heavier noble gases have higher melt-boil points .
what can polar substances dissolve in
polar covalent solvents (water - alcohols) will dissolve in
- ionic compounds
- polar covalent compounds
what will non- polar (alkanes) covalent solvents dissolve in
they will dissolve in other non-polar substances
eg candle wax or oil
what phrase should we remember when it comes to solubility
LIKE DISSOLVES IN LIKE
what is viscosity
the viscosity of liquids increases as the intermolecular forces increase,
- as the number of of hydrogen bonds in a substance increases the viscosity increases
substances with hydrogen bonding will be more viscous than substances with no hydrogen bonding
presence of which bonds will imply hydrogen bonding
O-H , N-H , F-H will imply hydrogen bonding
