Shapes of molecules + Electronegativity Flashcards
What do solid lines represent when drawing shapes of molecules
Tells us that these two bonds lie on the plane of the screen or page
In methane - the two hydrogen atoms also lie on plane of the page
What does a solid wedge show
Tells us that this bond is coming out of the plane of the page
h atom is also coming out of the plane of the page
What does a dotted wedge tell us
Tells us that this bond is projecting back behind the plane of the page. this hydrogen is behing the plane of the page
Electron pair repulsion theory
The shape of a molecule is determined by the electron pairs surrounding the central atom (outer shell)
Based on the fact that each pair of electrons on an atom repels every other pair of electrons
Therefore, the pairs of electrons are spaced as far apart as possible to minimise this repulsion
covalent bond is pair of electrons
Draw BeCl2
State structure and bond angle
Be is covalently bonded to two atoms of Cl
This means that we have two electron pairs around the central atom
These two pairs of electrons repel each other and move as far apart as possible.
The furthest that they can move apart is in a straight line
Cl - B - Cl
Molecule has a linear structure
angle between these two bonds 180 degrees
Draw CO2
nAME structure and bond angle
carbon has two double bonds to o2 atoms, when looking at multiple bonds such as double or tripe bonds - to determine the shape of the molecule, we treat a multiple bond as a single bonding area
double bond is treated the same as single bond
the two bonding areas, repel and move as far apart as posssibel
angle between bonding areas - 180 degrees
Linear shape
Draw BF3
name structure and bonding angle
https://homework.study.com/cimages/multimages/16/bf3_straae3595b-656a-4413-b807-ac49a5eacc7f.png
trigonal planar (flat)
120 degrees
3 pairs of bonding electrons around it
Draw CH4
STRUCTURE AND BOND ANGLE
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRDzwPzHEiXxVIY3tSI4TzOjNZyZvEK1vcB5A&s
DASHED LINE BIG TO SMALL (CENTRAL ATOM TO SURRROUNDING ATOM)
OPPOSITE TO WEDGE
Four bonding pairs
Tetraheadral
109.5 degrees
Draw PCl5
https://general.chemistrysteps.com/wp-content/uploads/2022/08/PCl5-2.png
5 BONDING PAIRS OF ELECTRONS
Trigonal bipyramidal
90 degrees and 120 degrees
bonds up and down are 90 degrees
the angel between the bodns lying on the central plane is 120 degrees
Draw SF6
https://cdn1.byjus.com/wp-content/uploads/2022/12/sf6.png
Octahedral
90 degrees
Bonds are pointing up and down at 90 degrees to central plane
The angle between the bonds lying on the central plane is also 90 degrees
6 bonding pairs
Draw CO3 2-
https://homework.study.com/cimages/multimages/16/4441432345241837731705.png
o- o - WITHOUT SQUARE BRACKETS
120 DEGREES
TRIGONAL PLANAR
dRAW NITRATE ION
NO3 -
cENTRAL ATOM N
N -> O
N - O-
aT THE TOP
N = O
Trigonal planar
120 degrees
draw sulfate ion so4 2-
Tetrahedral
109.5 degrees
s GOING UP DOUBLE BOND O
To the sides double bond O
Dashed line O-
Wedge O-
State the different strengths of different types of repulsion
Lone pair–lone pair repulsion is greater than lone pair–
bond pair repulsion, which is greater than bond pair–bond
pair repulsion.
This extra repulsion decreases other bond angles by 2.5 degrees
Lone pairs repel more strongly than bonding pairs
draw nh3
3 bonding pairs + 1 lone pair
based on tetrahedral
called trigonal pyramidal
https://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/Ammonia-dimensions-from-Greenwood%26Earnshaw-2D.png/320px-Ammonia-dimensions-from-Greenwood%26Earnshaw-2D.png
reduced bond angle by 2.5 degrees
Bond angle - 107 degrees
Draw H2O
hAS 2 BOND PAIRS
2 LONE PAIRS
4 BONDING AREAS
COntains 2 lone pairs - each lone pair reduces bond angle by 2.5 degrees
104.5 DEGREES - 2 LONE PAIRS
Called V-shaped or bent molecules
Draw XeF6
Has 4 bonding pairs
2 lon epairs
Based on octrahedral 90 degrees
Square planar
https://edurev.gumlet.io/ApplicationImages/Temp/510444_0b46cf71-dfc4-4e23-a571-69be72f5bd86_lg.png?w=360&dpr=2.6
remember to circle lone pairs
What is electronegativity
Electronegativity is the ability of an atom to attract the
pair of electrons in a covalent bond.
in hcl why the electrons in the covalent bond are closer to cl than h
e- is covalent bond are much closer to hydrogen nucleus than chlorine nucleus
electron pair in covalent bond is more attracted to cl nuclei than hydrogen nuclei
this makes the cl atom slightly negative compared to the hydrogen atom ( delta positive and negative)
Because cl atoms is more electronegative than h atoms
explain why in h- h
electrons in covalent bond lie exactly midway between nuclei - have same electronegativity
lie exactly midway between nuclei - have same electronegativity
so pairs of electrons in covalent bond are equally attracted to the two hydrogen nuclei
Trend of electronegativity
Electronegativity increass as we approach the top right of the periodic table
increasing electronegative across period (going left to right)
increasing electronegativity going up the group (down to up)
most electronegative - F O CL N
Based on attraction between the electron pair and the nucleus of the atom in question
factors affecting electronegativity
Size of positive charge on the nucleus
Moving left to right across a period, the number of protons in nucleus increases
THis increased positive charge increases the attraction between the nucleus and the pair of electrons in covalent bond
So elements on right of periodic table are more electronegative than those on the left
]Atomic radius ( distance from nucleus to outer shell)
The smaller the atomic radius, the closer the bonding electrons will be to the nucleus of an atom
AS WE MOVE LEFT TO RIGHT ACROSS A PERIOD, ATOMIC RADIUS DECREASES - means elements on right of periodic table are more electronegative than
those on the left.
Shielding of the nuclear charge by electrons in inner shells
Electrons in inner shells shield/screen electrons in outer shells from the positive charge of the nucleus
So because of this, the greater number of shells, the lower the electronegativity
therefore flourine which has 1 less inner electron shell than chlorine is more electronegative
Draw Delta positive and negative on H-CL
h - DELTA POSITIVE
CL - DELTA NEGATIVE
The electron pair has only shifted towards the more electronegative atom
delta negative - go on more delta negative
explain why co2 is a non-polar molecule despite having polar bonds
Both Carbon to oxygen double bonds are polar
These bonds point in opposite directions in a straight line
This means that their dipoles cancel each other out
because of this co2 has no overall polarity
separation of charge _____
called a dipole
Is hCL polar
Contains 1 covalent bond
This bond is polar
therefore molecule is polar
has a dipole moment (this overall polarity is called a dipole moment)
What is a polar molecule
A molecule in which the charge is not symmetrically distributed between the two atoms
One area is slightly positively charged, and another is slightly negatively charged
What is bond POLARITY
Bond polarity is the unequal sharing of electrons in a covalent bond -
extra….
due to differing electronegaitivies of atoms
what is a dipole moment
The overall effect of polar bonds in a molecule
when molecule is polarised overall (it has a slightly positive area and a slightly negative area ) - it has a dipole moment
is CCL4 polar molecule
Contains 4 c to cl bonds which are polar
Molecule is symmetrical in all directions, so dipoles cancel each other out
therefore molecule is non polar
Is CHCL polar
C - H bond is non-polar - have very similar electronegativities
Dipoles on c - cl bonds cannot cancel
charge is not symmetrically distributed across molecule
therefore polar
H2o polar
Bonds are polar
water molecule has a non-linear shape
means that although these two bonds point in different directions - they are not acting in a straight line
because of this, the bond polarities cannot cancel
which makes water a polar molecule
molecules can have polar bonds but not a ______
molecules can have polar bonds but not a dipole moment
types of intermolecular forces
permanent dipole-dipole forces/interactions
van-der-Waals forces (induced dipole-dipole interactions/forces)
hydrogen bonding
when can covalent bonds be broken
when can they not be broken
when can they be broken - chemical reaction
extremely strong
covalent bonds are not affected at all when a substance boils
where do intermolecular forces act
intermolecular forces act between molecules
what are stronger intermolecular forces or covalent bonds
weak intermolecular forces < covalent bonds
strength of intermolecular forces
intermolecular forces are easily broken e.g. by high temperatures
describe what happens when we heat a simple molecular substance
When we heat a simple molecular substance
This causes the molecules to move faster
At a certain temperature, causes the intermolecular forces to break, which allows the molecules to move away from each other
change of state
e.g. liquid HCL turning to gas
