chem exam 2 - unit 4 electron configuration

electron configuration

the arrangement of electrons in the energy shells (energy levels)

electrons exist in layers called __ (energy levels)

shells

electrons will fill the shells nearest the __ first

• 1st (K) shell holds a maximum of __ electrons

• 2nd (L) shell holds a maximum of __ electrons

• 3rd (M) shell holds a maximum of __ electrons

equation to solve maximum # of electrons per shell: 2n²

n = number of shell layer

• nucleus

• 2

• 8

• 18

K SHELL:

subshell name: 1s

maximum # of electrons present in shell: 2

distribute the electron in the subshell: 1s²

L SHELL:

subshell name: 2s, 2p

maximum # of electrons present in shell: 8

distribute the electron in the subshell: 2s² and 2p^6

M SHELL:

subshell name: 3s, 3p, 3d

maximum # of electrons present in shell: 18

distribute the electron in the subshell: 1s²

N SHELL:

subshell name: 4s, 4p, 4d, 4f

maximum # of electrons present in shell: 32

distribute the electron in the subshell: 4s², 4p^6, 4d^10, 4f^14

shell: n = 4 , # of subshells = 4 , letters specifying subshells = s p d f

shell: n = 3 , # of subshells = 3 , letters specifying subshells = s p d

shell: n = 2 , # of subshells = 2, letters specifying subshells = s p

shell: n = 1 , # of subshells = 1, letters specifying subshells =

Aufbau principle

electrons in different orbitals are filled in the increasing order of their energy

Pauli Exclusion Principle

• no more than two electrons can occupy the same orbital

• two electrons in the same orbital must have opposite spins

Hund’s Rule

• every orbital in a sublevel is singly occupied before any orbital is doubly occupied

• all of the electrons in singly occupied orbitals have the same spin

steps for writing electron configurations

1. know the number of electrons: it is equal to the atomic number of the element (unless it is an ion)

2. follow the order of orbitals: use Aufbau diagram

   ex: Potassium (K) – Atomic Number 19

   • 19 electrons

   • Configuration:
     1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

ex: Bromine (Br) – Atomic Number 35

• 35 electrons

• Configuration:
  1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵

steps for electron configuration for cations (positive ion)

Find the electron configuration of Mg²+

Step 1: Find the electron configuration of neutral Mg atom.

• Mg (12) = 1s² 2s² 2p^6 3s²

  Step 2: If the ion is ‘cation (positive ion)’, then SUBTRACT the same number of electrons from the outermost shell (valence shell)

  • in this case, +2 is the charge

  • remove two electrons from outermost shell (Valence shell) → in this case it is 3s²

  • electron configuration of Mg2+ is now 1s² 2s² 2p^6

steps for electron configuration for anions (negative ion)

Find the electron configuration of P³-

Step 1: Find the electron configuration of neutral Phosphorous (P) atom

• P (15) = 1s² 2s² 2p^6 3s² 3p³

Step 2: If the ion is ‘anion (negative ion)’, then ADD the same number of electrons to the outermost shell (valence shell)

• in this case, -3 is the charge

• add three electrons to the outermost shell (valence shell) → in this case it is 3p³

• electron configuration of P³- is now 1s² 2s² 2p^6 3s² 3p^6

identifying the neutral element for electron configurations

• add up all the numbers in the superscripts

• match the sum value to an element with the same atomic number

ex: 1s²2s²

2+2 = 4

element with atomic number of 4 = Beryllium

identifying the charged element for electron configurations

• same exact counting steps as for a neutral element

• after that, ADD the ion charge if +, or SUBTRACT the ion charge if -, to the sum value

• match the new value to the atomic number of element with the ion charge amount with it

ex: Which ion with a +1 charge has the following electron configuration?

1s² 2s² 2p^6 3s² 3p^6 3d^10 4s² 4p^6

= Rb+1

ex: Which ion with a -2 charge has the following electron configuration?

1s² 2s² 2p^6 3s² 3p^6 3d^10 4s² 4p^6

= Se-2

Bohr’s model:

moving up, electrons __ energy

moving down, electrons __ light energy

• absorbs

• emits

Principal quantum number (n)

• known as n

• describes the main energy level occupied by the electron

• as n increases, the ‘size’ of atom increases too

• the bigger the value of n = the higher the energy

• n must be a positive integer value starting from 1 (n = 1,2,3 etc.)

• n will never be a negative integer or zero

Azimuthal quantum number (l)

angular momentum:

• specifies the shape of an orbital aka subshell

• for every principle shell (n), there are 1+ subshell

4 diff subshells:

1. s - “sharp”

2. p - “principle”

3. d - “diffuse”

4. f - “fundamental”

magnetic quantum numbers (ml)

• determines the orientation of the orbital

• represented by symbol: ml

spin quantum number (ms)

• symbol: ms

• does not depend on another quantum number

• designates direction of the electron spin

  • either a spin of +1/2 (shown by ↑) or -1/2 (shown by ↓)

• positive ms = electron of an upward spin (aka “spin up”)

• negative ms = electron of a downward spin (aka “spin down”)

valence electrons

• are the outermost shell electrons

• inner shell electrons = core electrons

• only VE can chemical bond

identifying valence electrons

the number equal to the last digit of the group in P table = their valence electrons

slide 42: how do you identify the valence electrons and core electrons of an element from the electron configuration?

ionization energy

energy needed to remove an electron from an atom

• ionization energy increases when the atomic radius decreases

how to find the ionization energy of elements

use the periodic trends:

• increases across a period (→ left to right) bc of more protons = more attraction = harder to remove electrons

• decreases down a group (↓ top to bottom) more electron shells = electrons farther from nucleus = easier to remove

ex: Who has higher IE: Mg or Na?

• Mg is to the right of Na → Mg has higher IE.

ex: Which has the lowest IE: Li, Na, or K?

• K is furthest down → K has the lowest IE

how to draw a lewis dot structure

represents the valence shell electrons

steps:

1. find element on P table

2. determine # of valence electrons by looking at the group

3. it starts at the right moving clockwise around symbol

ex: P (group 5)

slide 53: octet rule

tendency of atoms to prefer to have eight electrons in the valence shell

• atoms with less than 8 electrons in their valence shell either lose or gain electrons to form stable compounds

• only s and p orbitals are involved in octet rule

ex: Electron Configuration of Neon (Ne) 1s² 2s² 2p^6 octet state

ex: Electron Configuration of Argon (Ar) 1s² 2s² 2p^6 3s² 3p^6 octet state