5.1 - Electrons And Bonding
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What are electron shells?
Help us visualise the whereabouts of electrons in an atom
Features of electron shells
Shells are regarded as energy levels The energy increases as the shell number increases
What are electron shells made up of?
They are made up of atomic orbitals This a region around the nucleus that can hold up to two electrons with opposite spins
What are the four different atomic orbitals?
S P D F
What shape are each of the orbitals?
S - sphere P - dumbbell D - more complex F - more complex
How many electrons in each shell?
1 - 2 electrons 2 - 8 electrons 3 - 18 electrons 4 - 32 electrons
Where do the electrons come from in each shell? Which sub shells are present?
1 - 1s - 2 electrons 2 - 2s, 2p = 2 + 6 = 8 3 - 3s, 3p, 3d = 2 + 6 + 10 =18 4 - 4a, 4p, 4d, 4f = 2 + 6 + 10 + 14 = 32
How many orbitals in each shell?
1 - 1s orbital 2 - 1s, 3p orbitals 3 - 1s, 3p, 5d orbitals 4 - 1s, 3p, 5d, 7f orbitals
How many electrons can all orbitals hold?
2 electrons
Why do electron pairs have opposite spins?
Electrons are negatively charged and repel one another The spins help counteract the repulsion between the negative charges of the electrons
In what order are orbitals filled?
One electron fills each each orbital before pairing starts(same energy level) Prevents any repulsion between pairs until there are no further orbitals on that energy level
Which has a higher energy level, the 4s sub shell or the 3d sub shell?
The 3D sub shell, so it gets filled first
How would you write the shorthand notation for electron configuration?
Write symbol of a noble gas and write down the remaining configuration.
How do cations form?
Formed when atoms lose electrons
How do anions form?
When atoms gain electrons
What are common cations and anions?
Cations - metals, e.g Na+, Ca2+ Anions - non metals, e.g Cl-, 02-
Where are each of the sub shells found in the periodic table?
S-block —> left hand block of the table P-block —> right hand block of table D-block —> transition metals block(centre of table)
How to write configurations of ions
Cations - take away from natural config what the charge was Anions - add on to natural config what charge was
When does ionic bonding occur?
Between a metal and a non-metal
What is an ionic bond
The electrostatic attraction between oppositely charged ions. Held together in a lattice structure
How would you visualise ionic bonds or compounds?
Dot and cross diagrams
Structure of an ionic bond
Oppositely charged ions arranged in a giant ionic lattice structure Each ion attracts oppositely charged ions in all directions
Properties of ionic compounds
Solid at room temp/High MP/BP - strong electrostatic forces of attraction require more energy to break Soluble in polar molecules - polar molecules able to break down the lattice and surround each ion in solution Conduct electricity when dissolved or molten - As a solid ions are in fixed positions, no mobile charge carriers When molten or dissolved, ionic lattice breaks down, so ions are free to move as mobile charge carriers
What is a covenant bond?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms