AS - Unit 1 - Electrons, bonding and structure Flashcards
What is the definition of first ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
What is electron shielding?
The repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons
What is the energy needed to form positive ions known as?
Ionisation energy
What is the first ionisation energy for sodium gas?
Na (g) ——–> Na+ (g) + e-
The nuclear attraction experienced by an electron depends on what three factors?
Atomic radium
Nuclear charge
Electron shielding or screening
How does atomic radius affect nuclear attraction?
The greater the atomic radius the smaller the nuclear attraction experienced by the outer electrons
How does nuclear charge affect nuclear attraction?
The greater the nuclear charge the greater the attractive force on the outer electrons
How does electron shielding or screen affect nuclear attraction?
The inner shell electrons repel the outer shell electrons
The repelling is called electron shielding
the more inner shells there are, the larger the shielding effect and the smaller the nuclear attraction experienced by the outer electrons
What are successive ionisation energies?
A measure of the energy required to remove each electron in turn
What is second ionisation energy?
The energy required to remove one electron from each ion in one mol of gaseous 1+ ions to form one mol of gaseous 2+ ions
Why does ionisation energy increase after each level?
Because as each electron is removed there is less repulsion between the electrons and each shell will be drawn in to be slightly closer to the nucleus
as the distance of each electron from the nucleus decreases slightly, the nuclear attraction increases.
Give the definition of a shell
A group of atomic orbitals with the same principal quantum number. Also known as a main energy level
Give the definition for principal quantum number
A number, n, representing the relative overall energy of each orbital, which increases with distance from the nucleus
The sets of orbitals with the same n-value are referred to as electron shells or energy levels
How many electrons are there in the first shell?
2
How many electrons are there in the second shell?
8
How many electrons are there in the third shell?
18
How many electrons are there in the fourth shell?
32
what is an atomic orbital?
A region within an atom that can hold up to two electrons with opposite spins
What are the four different types of orbitals?
s, p, d and f
What shape is an s orbital?
Spherical
Where are the s orbitals present?
from n=1 upwards, each shell contains 1 s orbital.
How many s electrons are there in each shell?
2
What shape is a p orbital?
A three dimensional dumb-bell shape
Where are the p orbitals present?
from n=2 upwards
each shell contains three p orbitals all at right angles to each other
how many p electrons are there in each shell?
6
Where are d orbitals present?
from n=3 upwards
each shell contains five d orbitals
How many d electrons are there in each shell?
10
Where are f orbitals present?
from n=4 upwards
each shell contains 7 f orbitals
how many f electrons are there in each shell?
14
What is the only way that two electrons can fit in the same orbital?
if they have opposite spins
How to electrons occupy orbitals
like bus seats
each electrons will take up an empty orbital in that sub-shell until all orbitals have one electrons in, then they double up
How do electrons occupy sub-shells?
in order of increasing energy levels
What is the electronic configuration of boron?
1s2 2s2 2p1
What is the electronic configuration of oxygen?
1s2 2s2 2p4
Explain the 3d 4s sub-shell overlap
The 4s sub-shell has a lower energy level than the 3d sub-shell
the 4s-orbital fills before the orbitals in the 3d sub-shell
the 4p-orbital starts to fill after the 3d-orbital is full
The larger the value of principal quantum number the ……
higher the energy level and the further the shell is from the nucleus
On the periodic table which elements are included in the s block?
group 1 and 2
On the periodic table which elements are included in the p block?
groups 3 - 8/0
on the periodic table which elements are included in the d block?
the transition metals
For atoms with many electrons how is the electronic configuration abbreviated?
by naming the noble gas which comes before it and then continuing with the electronic configuration from there
how do you alter the electronic configuration for ions?
if it is a negative ion, electrons have been added meaning the electronic configuration would increase 1 place for a 1- ion
if it is a positive ion, electrons are lost meaning the electronic configuration would decrease 1 place for a 1+ ion
What are the exception to the rule ions which you need to be aware of and how do they change?
Sc and Zn, at the top of the d-block
after the 4s orbital has been filled it is actually at a higher energy level so the 4s electrons are lost before the 3d level
What are with 6 noble gases?
helium, He neon, Ne argon, Ar krypton, Kr xenon, Xe radon, Rn
Give two properties of noble gases regarding electrons?
all electrons are paired, with opposite spins
the outer shell contains 2 electrons (for He0 or 9 electrons (for all other noble gases)
Give a property of an atom with a full outer shell
very un-reactive
What is the octet rule?
The tendency to acquire a noble gas electron configuration, where all 8 electrons make up the outer shell, even if that means sharing one or two
What are the three types of chemical bonds?
ionic, covalent and metallic
What is a compound?
a substance formed from two or more chemically bonded elements in a fixed ratio, usually shown by a chemical formula
In general where does ionic bonding occur?
in compounds consisting of a metal and non metal
How does ionic bonding work?
Electrons are transferred from the metal atom to the non metal atom to form oppositely charged ions that attract
where does covalent bonding occur?
in compounds consisting of two non-metals
Explain covalent bonding
electrons are shared between the atoms in order to complete the octet
Explain metalic bonding
electrons are donated from each metal ion to form a sea of delocalised electrons which will hold all the metal ions together
Give 4 facts about noble gases
makes up about 1% of air
in air argon is the most abundant
30 times more argon than carbon dioxide in the air
all noble gases (except radon) can be separated by the fractional distillation of liquefied air
Give a use of helium
used in air ships
give a use of neon
advertising signs
give a use of argon
used in filament light bulbs
give a use of krypton
used in lasers for eye surgery
give a use of Xenon
used in car headlights
What is an ionic bond?
the electrostatic attraction between oppositely charged ions
Which way are electrons transferred in ionic bonding?
from the metal atom to the non metal atom
What is a giant ionic lattice?
A three dimensional structure of oppositely charged ions, held together by strong ionic bonds
What is a covalent bond?
a bond formed by a shared pair of electrons
What is a lone pair?
An outer shell pair of electrons that is not involved in chemical bonding
What is a dative covalent bond?
a shared pair of electrons which has been provided by one of the bonding atom only
Which two elements from period 2 don’t reach a full outer shell?
Beryllium Be
Boron B
Which groups in the periodic table can expand the octet?
5-7
Atoms of non metals in group 5 can form how many bonds?
3 or 5 covalent bonds
Atoms of non-metals in group 6 can form how many bonds?
2, 4, or 6 covalent bonds
Atoms of non-metals in group 7 can form how many bonds?
1, 3, 5 or 7 covalent bonds
Give an example of an atom which expands the octet?
Sulfur
it has 6 electrons in its outer shell so each electron covalently bonds with a flourine forming 6 covalent bonds meaning 12 electrons in sulfurs outer shell and 8 in the outer shell of each flourine
Describe a better rule than the octet rule
unpaired electrons pair up
a maximum number of electrons that can pair up is equivalent to the number of electrons in the outer shell
Explain the electron-pair repulsion theory
As electrons all have a negative charge, each electron pair repels other electron pairs
The electrons pairs push each other as far apart as possible
What is the bond angle for a trigonal planar molecule?
120 degrees
what is the bond angle for a tetrahedral molecule?
109.5 degrees
What is the bond angle for an octahedral molecule?
90 degrees
Which electron pairs repel more?
lone pair/lone pair > bonded pair/lone pair > bonded pair/bonded pair
What is the bond angle for a pyramidal molecule?
107 degrees
What is the bond angle for a non-linear molecule?
104.5 degrees
Give an example of a tetrahedral molecule
methane
give an example of a pyramidal molecule
ammonia
give an example of a non-linear molecule
water
What is the bond angle of a linear molecule?
180 degrees
give an example of a linear molecule
CO2 (something with a double bond)
What is electronegativity?
a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
What is a permanent dipole?
a small charge difference across a bond that results form a difference in the electronegativities of the bonded atoms
What is a polar covalent bond?
a bond that has a permanent dipole
What is a polar molecule?
A molecule that has an overall dipole, when you take into account any dipoles across the bonds
Which way does electronegativity move on the periodic table?
up and right, the most electronegative molecule being helium
Rate the different kinds of bonds in terms of strength
ionic and covalent > hydrogen > dipole-dipole > van der Waals’
What is an intermolecular force?
The force of attraction betweek neighbouring molecules
What is a permanent dipole-dipole force?
A weak attractive force between permanent dipoles in neighbouring polar molecules
What are van der Waals’ forces?
Forces of attraction between induced dipoles in neighbouring molecules
What is the corellation between electrons, boilding point and intermolecular forces
electrons increase
ven der waals’ forces increase
boiling point increases
How does boiling point change throughout the nobel gases?
It increases as we go down the group
What is a hydrogen bond?
a strong dipole dipole attraction between :
an electron deficient hydrogen atom on one molecule
a lone pair of electrons on a highly electronegative atom
Why is ice less dense than water?
Ice has an open lattice with hydrogen bonds holding the water molecules apart
when ice melts the rigid hydrogen bonds collapse allowing the H2O molecules to move closer together
Why does water have a relatively high boiling and melting point?
Because the hydrogen bond strength is higher than the strength of van der Waals’ forces meaning in order to break those bonds to melt or boil you have to put in a lot more energy
What is metallic bonding?
The electrostatic attraction between positive metal ions and delocalised electrons
What is a giant metallic lattice?
A three-dimensional structure of positive ions and delocalised electrons, bonded together by strong metallic bonds
Give 3 properties of metallic lattices
High melting and boiling points
Good electrical conductivity
Metals are ductile and malleable
what happens to giant ionic lattices when they dissolve in water?
The ionic bonds are split up and water molecules surround each ion
what is a giant covalent lattice?
a three-dimensional structure of atoms, bonded together by strong covalent bonds
what is a simple molecular lattice?
a three-dimensional structure of molecules, bonded together by weak intermolecular forces
Give 3 properties of simple molecular structures
Low melting and boiling point
Electrical conductivity
Solubility
Give 3 properties of giant covalent structures
high melting and boiling point
electrical conductivity
solubility
What is the structure of diamond?
tetrahedral
What is the conductivity of diamond?
Poor conductivity
What is the structure of graphite?
Strong hexagonal layer structure with weak van der Waals’ forces between layers
What is the electrical conductivity of graphite??
Good conductivity due to the delocalised electrons between the layers
What is the hardness of diamond?
Hard!
The tetrahedral shape allows external forces to be spread throughout the lattice
What is the hardness of graphite?
Soft
bonding within each layer is strong
however weak forces between layers allow layers to slide easily
