Module 2 Section 2: Electrons, Bonding and Structure Flashcards
Nature of electrons and how they move around the nucleus
Electrons have fixed energies
They move around the nucleus in shells ( sometimes called energy levels )
These shells are all given numbers known as principal quantum numbers
How does energy change in shells with distance from the nucleus
Shells further from the nucleus have a higher energy ( and a larger principal quantum number ) than shells closer to the nucleus
Arrangement of electrons
The electrons shells are divided into sub - shells
Different electron shells have different numbers of sub-shells, each of which has a different energy
Sub-shells are called s-, p-, d- or f sub shells ( just need to acknowledge f-sub-shell )
These sub-shells have different numbers of orbitals, which can hold up to 2 electrons
The numbers of electrons that can fit into each sub shell
S sub-shell: 1 orbital, 2 max electrons ( 1 x 2 = 2)
P sub-shell: 3 orbitals, 6 max electrons (3 x 2 = 6)
D sub-shell: 5 orbitals, 10 max electrion (5 x 2 = 10)
F sub shell: 7 orbitals, 14 max electrons (7 x 2 = 14)
Structure of first 4 shells
1st: 1s - 2 total electrons
2nd: 2s 2p - 8 total electrons
3rd: 3s 3p 3d - 18 total electrons
4th: 4s 4p 4d 4f - 32 total electrons
What is an orbital
A region within an atom (around the nucleus - spec) that can hold up to two electrons with opposite spin
Orbitals within the same sub-shell have the same energy
What happens when there are two electrons in the same orbital
They must ‘ spin ‘ opposite directions
This is called spin-pairing
Shapes of orbitals
s orbitals are spherical
p orbitals have dumbbell shapes
There are three p orbitals and they’re at right angles to one another
What is electron configuration
The number of electrons an atom or ion has, and how they are arranged
Different ways to show electron configuration
Sub shell notation: 1s^2 2s^2 2p^6
Big number: energy shell level ( principal quantum number )
Letter: sub shell
Superscript: number of electrons
Electrons in boxes
Each box represents an orbital and each arrow is an electron
The up and down arrows show electrons spinning in opposite directions
Two electrons can only occupy the same orbital if they have opposite spin
E.g. 1s: ⬆️⬇️, 2p: ⬆️⬇️ ⬆️⬇️ ⬆️⬇️
Exception with 4s and 3d sub shell
Even though 4s’ quantum number is bigger than 3d, it has a lower energy level than 4s
This means 4s fills up first
This has exceptions as well ( copper and chromium )
How to fill out an atoms electron configuration
Electrons fill up the lowest energy sub-shells first
Electrons fill orbitals with the same energy singly before they start sharing
For the configuration of ions from the s and p blocks of the periodic table, just remove or add the electrons to or from the highest energy occupied sub shell
E.g. Mg2+: 1s2 2s2 2p6
E.g. Cl-: 1s2 2s2 2p6 3s2 3p6
note that when losing electrons, electrons are lost from 4s before 3d (the energy levels are very close, and when electrons fill them, 4s goes above 3d). “
How can noble gases be used in electron configuration
Can be used in shorthand configuration
E.g. calcium: 1s2 2s2 2p6 3s2 3p6 4s2 can be written as [Ar]4s2
( Ar: 1s2 2s2 2p6 3s2 3p6 )
How are ions formed
When electrons are transferred from one atom to another so as to have full outer shells
They may positively or negatively charged
How are ions held together
Electrostatic attraction holds the positive and negative ions together
When atoms are held together like this, it’s called ionic bonding
What is ionic bonding
An ionic bond is an electrostatic attraction between two oppositely charged ions
What happens when two oppositely charged ions bond
When oppositely charge ions form an ionic bond, you get an ionic compound
The formula for an ionic compound tells you what ions that compound has in it
E.g. KBr is made of K+ and Br- ions
Why are ionic compounds neutrally charged
The positive charges in the compound balance the negatively charges exactly so the overall charge is zero
How are dot and cross diagrams helpful
They show the arrangement of electrons in an atom or ion
Each electron is represented by a dot or a cross
They can show which atom the electrons in a bond originally came from
Structure of ionic compound e.g. sodium chloride
The Na+ and Cl- ions are packed together alternately in a regular structure called a lattice
The structure’s called ‘ giant ‘ because it’s made up of the same basic unit repeated over and over again
It forms because each ion is electrostatically attracted in all directions to ions of the opposite charge
The sodium chloride lattice is cube shaped - different ionic compounds have different shaped structures
Sodium chloride’s got very strong ionic bonds, so it takes lots of energy to break up the lattice
This gives it a high melting point (801°C)
When do ionic compounds conduct electricity
Ionic compounds conduct electricity when they’re molten or dissolved - but not when they’re solid
The ions in a liquid are mobile (and they carry a charge)
In a solid they’re fixed in position by the strong ionic bonds
Why do ionic compounds have high melting and boiling points
The giant ionic lattices are held together by strong electrostatic forces
It takes a lot of energy to overcome these forces, so their melting and boiling points are very high
Why do ionic compounds dissolve in water
Water molecules are polar - part of the molecule has a small negative charge and the other parts have small positive charges
The water molecules are attracted to the charged ions
They pull the ions away from the lattice and cause it to dissolve
(When ions in compound have a large charge it will be insolvable and sparingly soluble because the attraction may be too strong for the molecules to break down the ionic structure.)
When do molecules form
Molecules form when two or more atoms bonds together
It doesn’t matter is the atoms are the same or different
Examples of common molecules
Chlorine gas: Cl2
Carbon Monoxide: CO
Water: H2O
Ethanol: C2H5OH
How are molecules held together
Molecules are held together by covalent bonds
In covalent bonding, two atoms share electrons, so they’ve both got full outer shells
What is a covalent bond
A covalent bond is the strong electrostatic forces of attraction between a shared pair of electrons and the nuclei of the bonded atoms
What are the exceptions that we must know for covalent molecules
A few compounds have less than 8 electrons in their outer shell ( electron deficient )
In boron trifluoride, boron only has 6 electrons in its outer shell
Some compounds can use d orbitals to expand the octet
This means they have more than 8 electrons in their outer shell
In sulfur hexafluoride, sulfur has 12 electron in its outer shell
What is average bond enpalthy
Average bond enpalthy measures the energy required to break a covalent bond
The stronger the bond is, the more energy is required to break it, and so the greater the value of the average bond enpalthy
Covalent double and triple bonds
Some atoms can form double and triple covalent bonds
These multiple bonds contain more than one shared pair of electrons between two atoms
An example of a double bond is oxygen ( O2 )
What type of covalent bonds is measured in nitrogen and carbon dioxide molecules
Nitrogen has 5 electron in it’s outer shell, so it needs another 3 to have a full outer shell
This is done by each nitrogen atom shares 3 electrons - resulting in a triple bond
Carbon has 4 elections in its outer shell, so it needs another 4 to have a full outer shell
This means each oxygen atom must share 2 electrons