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chemistry unit 1 > periodicity > Flashcards

periodicity Flashcards

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1
Q

how are elements arranged in the periodic table

A

in increasing atomic number

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2
Q

what happens when you go down a group in the table

A

vertical columns within the table contain elements with similar chemical properties resulting in a common number of electrons in the outer shell

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3
Q

what happens when you go across a period in the table

A

rows of elements arranged with increasing atomic number, demonstrating an increasing number of outer electrons and a move from mettalic to non-metallic characteristics

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4
Q

what happens to the atomic size {covalent radius} as you go across a period

A

it decreases due to the increasing positive nuclear charge and there is a greater attraction between the increasing n.o of protons and electrons

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5
Q

what happens to the covalent radius as you go down a group

A

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

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6
Q

what is the ionisation energy

A

ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms.

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7
Q

what happens to the ionisation energy as you go across a period

A

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

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8
Q

what happens to the ionisation energy as you go down a group

A

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.

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9
Q

what is electronegativity

A

electronegativity is a measure of attraction for electrons in a covalent bond

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10
Q

what happens to the electronegativity across a period

A

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

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11
Q

what happens to the electronegativity as you go down a group

A

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

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12
Q

what is metallic bonding

A

electrostatic force of attraction between positively charged ions and delocalised electrons

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13
Q

what elements are metallic

A

Li , Be , Na , Mg , Al , K , Ca ,

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14
Q

what is ionic bonding

A

electrostatic force of attraction between positive ions of one element{normally a metal} an the negative ions of another element { normally a non-metal]

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15
Q

what is a covalent bond

A

a covalent bond is the result of 2 positive nuclei being held together by there attraction for a shared pair of electrons

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16
Q

give examples of covalent molecular

A

H2, N2, O2 , F2 , Cl2 , P4 , S8 ,

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17
Q

what is a polar covalent bond

A

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

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18
Q

what is a non polar bond

A

non polar covalent bonds are formed between atoms with the same electronegativities.

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19
Q

how do you detect polar covalent structures

A

polar covalent liquids are attracted to charged rods eg. a stream of water is deflected by a charged rod .

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20
Q

what is the bonding continuum uses for

A

used to understand different types of bonding by observing variations in electronegativity between atoms

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21
Q

what does the bonding continuum show us

A

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

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22
Q

what happens to molecules with symmetrical arrangements

A

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

23
Q

`how do intermolecular forces occur

A

the occur between atoms and molecules they are weak

24
Q

where do intramolecular forces occur

A

bonds inside the molecule

25
Q

what are the 3 type of van der waals’ forces

A

london dispersion forces
permanent dipole-permanent dipole interactions
hydrogen bonds

26
Q

properties of london dispersion forces

A
  • 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.
27
Q

what is the definition for LDF

A

LDF are the electrostatic forces of attraction between temporary and induced dipoles caused by the movement of electrons

28
Q

what happens when an atom has a temporary dipole and induced dipole

A

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

29
Q

what has the strength of LDF got to do with the electrons

A

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

30
Q

example of melt/boiling point in the noble gases group in regard to LDF

A

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.

31
Q

what is permanent dipole-permanent dipole interactions

A

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
32
Q

what is hydrogen bonding

A

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

33
Q

what is the strongest type of intermolecular force

A

hydrogen bonding is the strongest type of intermolecular force but note that it is still weaker than a covalent bond.

34
Q

what do water , hydrogen fluoride and ammonia have in common

A

HF , H2O, NH3 , all have anomalous boiling points due tot the presence of hydrogen bonding.

35
Q

how is ice dense

A

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.

36
Q

where are the intramolecular forces

A

in polar covalent and non-polar covalent molecules [inside the mol]

37
Q

what are the intermolecular forces

A

LDF , PD-PD interactions , Hydrogen bonds

38
Q

what do monatomic structures consist of

A

they consist of discrete (individual) atoms held together by london dispersion forces

39
Q

what do covalent molecular structures consist of

A

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
40
Q

give examples of covalent molecular compounds

A

ammonia water methane and carbon dioxide

41
Q

what do covalent network structures consist of

A

covalent network structures consist of giant lattice of atoms covalently bonded to each other , elements such as boron, silicon and some forms of carbon

42
Q

tell us about carbon atom

A

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.

43
Q

tell us about graphite covalent network

A

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

44
Q

what is fullerenes - covalent molecular structure

A

are made up of large molecules containing between 60-80 carbon atoms
-they have covalent molecular structures with weak LDF between the molecules

45
Q

why does -element 1- have a higher melting point than element 2

A

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.

46
Q

what do the melting and boiling point depend on

A

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

47
Q

do metals and ionic compounds have high or low melt-boil points

A

both metal and ionic compounds have high melt-boil points due to large lattice structures they have

48
Q

do covalent network structures have high or low melting -boiling points

A

tend to have high melt-boil points due to strong covalent bonds have to be broken

49
Q

noble gases melt boiling point

A

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 .

50
Q

what can polar substances dissolve in

A

polar covalent solvents (water - alcohols) will dissolve in

  • ionic compounds
  • polar covalent compounds
51
Q

what will non- polar (alkanes) covalent solvents dissolve in

A

they will dissolve in other non-polar substances

eg candle wax or oil

52
Q

what phrase should we remember when it comes to solubility

A

LIKE DISSOLVES IN LIKE

53
Q

what is viscosity

A

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

54
Q

presence of which bonds will imply hydrogen bonding

A

O-H , N-H , F-H will imply hydrogen bonding

chemistry unit 1 (1 decks)

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