Atomic structure

Question 1

definition of Atoms

Answer 1

smallest quantity of matter, basic unit of element , cannot be broken down into 2 or more simpler substance

In atoms : number of proton will be the same as the number of electron if atoms are neutral

Question 2

Subatomic particles

Answer 2

found in nucleus of atom:
Proton (+)
neutron (0)

found around nucleus of atom:
electron (-)

Question 3

Atomic Number , Mass number, Isotopes

Answer 3

atomic number :

symbol: Z
refers to the no. of proton in nucleus and this will determine the identity of an element

mass number :

symbol :A , S.I unit : amu
refers to the total number of proton and neutrons

isotopes :
refers to element with same atomic number (Z) but different mass number (A)
(these element will exhibit very similar properties with one another due they share same number of protons and electrons )

Question 4

Relative atomic mass

Answer 4

refers to the average mass of naturally occurring moisture of isotopes

S.I unit : amu

calculate :
(natural abundance /100 x amu ) + (natural abundance /100 x amu )

Question 5

main group element of periodic table and the specific 4 group with names

Answer 5

main group element are elements that is not the transition element group and inner transition elements

group 1A : alkali metal
group 2A : alkali earth metal
group 7A : halogens
group 8A : noble gasses

Question 6

Periodic table

Answer 6

horizontal - period ( increasing atomic number (Z) across period from left to right )

vertical - group ( increasing size of atom going down the group)

Question 7

Energy level(electron shell) and electrons

Answer 7

electrons are quantised, and they only can have a certain,definite amount of energy

electrons are restricted to certain energy level (each level represent a permitted or allowed amount of energy )

energy level : arranged into main level that is determined by principal quantum number (n)

n- related to distance if the electrons from the nucleus , larger the n , larger the average distance of electrons from nucleus

Question 8

Ground and excited state of electron

Answer 8

ground state : electron occupies the lowest energy level available

excited state: electron absorb a discrete amount of energy and move to a higher energy level (n)

n can only be positive whole number

Question 9

energy sub level / subshell

Answer 9

each energy level (shell) is composed of one or more subshells or sub level this is specified by a secondary quantum number (I)

the S,P,D,F (also known as subshell ) is used to specify value of I and the subshell within a shell is differ slightly in energy

SPDF Are subshell and they also tell us the shape of the region of space electron might be found

and each subshell is composed of one or more atomic orbital :

S-1 orbital
P-3 orbital
D-5 orbital
F-7 orbital

highest energy is F and lowest is S

Question 10

Atomic orbital

Answer 10

a region of space within the electron subshell where electrons are most likely to be found

Question 11

shape of the subshell or orbital of S and P

Answer 11

S (sharp) orbital - spherical in shape but different in size, size increase w increasing n , one orbital present only

P (principal) orbital - dumbbell in shape , 3 orbital present (lie at 90 degree to one another Pxyz )

Question 12

Pauli exclusion principle

Answer 12

each orbital can only hold up to a maximum of 2 electrons which must be of opposite spin

Question 13

Aufbau principle

Answer 13

Electrons will fill up the lowest sub energy level to capacity before filling orbitals of a higher sub energy :

lowest -> highest energy
s p d f

Question 14

electron configuration and orbital diagram

Answer 14

electron configuration :
shell, subshell to the power of number of electron in subshell

e.g 1s^2

orbital diagram :
no more box and dot diagram instead use box to represent an atomic orbital and arrows to represent electrons and below the box , label the orbital

do note : both electron configuration and orbital diagram can be represented using noble gases configuration (short cut)

Question 15

Hund rule

Answer 15

for orbital of equal energy(also known as degenerate) , the electron will occupy each orbital first before pairing up

e.g in p subshell, there is 3 orbital, these orbits are drew tgt to denote equal energy level and electrons will fill all 3 orbital first before the remaining electrons pair up w others in the orbital

Question 16

deviation from Aufbau principal

Answer 16

aufbau principal: electron will fill up orbitals of lowest sub energy to capacity before filling orbital of higher sub energy

deviation is only possible between the 4s and 3d subshell ( Chromium (Cr) and Copper (Cu) ) and the elements directly below Cr and Cu

Question 17

Deviation reason from the aufbau principal

Answer 17

Cr : there is slightly greater stability of d subshell that are half filled (d5) . since the 4s and 3d subshell have almost similar energy level and the electron occupy the orbital singly to ease the electron electron repulsion

Cu : there is slightly greater stability of d subshell that are completely filled (d10)

Question 18

Valence electron and isoelectronic

Answer 18

Valence electron
- outmost electron of an atom, these electrons are involved in formation of chemical bond

cation : neutral atom lose an electron
anion : neutral atom gain an electron

isoelectronic 
- a group of atoms /ions that have the same number of electrons with same configuration