Chapter 7 - Periodicity Flashcards
a period is a ?
row across the periodic table. All elements in the same period have the same number of shells
A group is ?
the column going down the table. Elements in the same group have their outer electron in the same position e.g. group 1 elements have their outer electron in the 2s orbital
periodicity is?
a repeated trend in properties across any period of the periodic table
trends in electron configuration across periods 2 & 3?
order in which subshells fill up
s -> p -> d
properties across a period?
- across a period, type of structure/ bonding changes
- metallic -> giant covalent -> simple molecular -> monatomic
- electrical conductivity changes - metallic yes, ionic sometimes, covalent, no except graphite
melting/ boiling point across a period?
depends on the type of structure/ bonding
- metallic = high, giant covalent = very high, simple molecular = low
atomic radius definition?
Atomic radius is related to the distance from the nucleus of an atom to the outer shell electron. The larger the atomic radius, the larger the atom
nuclear charge?
the more protons in the nucleus, the more strongly outer electrons are attracted, the smaller the atomic radius
shielding?
- the repulsion between electrons in inner shells reduces the attraction the outer electrons feel from the nucleus
- SAME ACROSS PERIOD
why does atomic radius decrease across periods?
- bigger nuclear charge pulls outer electrons closer to the nucleus
- shielding stays the same
- the increasing no. of outer electrons are all in the same shell
why does atomic radius increase down a group?
- NC increases
- s increases
- number of shells increases so attraction between nucleus & outer shell electrons decreases
first Ionisation Energy equation ?
Na (g) - e (^-) -> Na plus (g)
STATE SYMBOLS
1st IE definition?
the energy required to remove one electron from each atom in one mole of gaseous atoms to form gaseous 1+ ions
why is energy needed for the 1st IE
overcome the attractive force between the nucleus and the electron that is being removed
effect of increasing nuclear charge on 1st IE?
- Higher IE = more energy needed to remove the electron as electron more strongly attracted
effect of increasing atomic radius on 1st IE?
lower IE
as electron is further away from pull of nucleus
effect of increasing shielding on 1st IE?
lower IE
as outer electron feels attraction of nucleus less
trends in 1st IE across period 3?
- IE increases
as NC increases, Shielding stays same, Atomic radius decreases - outer e are attracted to nucleus more strongly
- more energy needed to remove em
irregularities in 1st IE can be explained in terms of ?
electron arrangement
Why is less energy needed to remove 1 electron from Al?
the 3p electron is further away from nucleus than the 3s electrons so less strongly attracted, therefore lower energy to remove 3p electron.
why is less energy needed to remove 1 electron from S?
removing this electron removes the repulsion between 2 electrons in one p orbital therefore requires less energy
– this always happens when removing 4th electron from p subshell
summary of trends across period 3?
- Atomic radius decreases
- 1st IE increases
- MP& BP - increase to a max., decreases sharply
if enough energy is applied, all ….
electrons can be removed from an atom
definition: 2nd IE?
energy needed to remove 1 electron from each ion in 1 mole of gaseous atoms forming one mole of gaseous 2+ ions
why do successive IE increase?
as we remove e-, the proton: electron ratio increases and electrons are attracted more strongly by the nucleus, decreasing the radius of the ION.
successive IE: new shell?
when removing an electron breaks into a new shell, there will be a large increase in IE bc atomic radius & shielding both decrease
trends in 1st IE across period?
- 1st IE increases
- NC increases
- AR decreases
- S stays same
- e- more strongly attracted to nucleus, more energy needed
trends in 1st IE down group?
- IE decreases
- NC increases (eventho), Ar & S increase (also)
- e- weakly attracted to nucleus, less energy
what is ionisation energy?
measures how easily an atom loses electrons to form positive ions
successive IEs allow predictions to be made about?
- the number of electrons in the outer shell
- the group of the element in the periodic table
- the identity of an element
PD structure: elements are arranged in order of?
increasing atomic number
PD structure: elements within a group have?
same number of electrons in outer shell so
similar chemical properties
as chemical reactions involve outer shell electrons
PD structure: s block?
- Groups 1,2 and He
- highest energy electron is held in an s block
PD structure: p block?
- groups 3-8
- highest energy electron held in p block
PD structure: d block?
- Period 4: Sc to Zn
- Period 5: Y to Cd
PD structure: what are metalloids?
elements that touch the stepline between metals and non-metals
- show both metallic & non- metallic properties
PD structure: why is hydrogen an unusual case?
- non metal, often included in G1 as has 1 electron in outer shell
what is ionisation energy?
the energy required to completely remove an electron from an atom of an element
general trends in IE across a period and group?
- Period: increase
- group: decrease
