Chapter 5 +6 electrons, bonding and shapes of molecules Flashcards
Define ionic bonding
The electrostatic attraction between oppositely charged ions
For electronic configuration when there is a negative ion you _____ the number of electrons _____ the configuration. When there is a positive ion you _________ the number of electrons ____ the configuration but 4s _____ before 3d
Add Onto Take away From Empties
Positive ions from when
An atom usually a metal looses one or more electrons
Negative ions form when
An atom usually a non metal gains one or more electrons
Dot and cross diagrams often only show a ______ number of ions, however in an ionic substance the attraction between oppositely charged ions will happen in _________ ____________
Small All directions
The structure of ionic substances is called a
Giant Ionic lattice
Are melting points of an ionic substance high or low?
High
What state are ionic substances in at room temperature
Solid
Why do ionic substances have high melting and boiling points?
Because a large amount of energy is needed to overcome the strong electrostatic attraction which occurs between oppositely charged atoms throughout the lattice
Which has a higher melting point? CaO or CaF2
Cao
Explain why an ionic structure made with 2+ and 2- ions will have a higher melting point than one with 1+ and 1- ions
Because the electrostatic attraction between the 2+ and 2- ions is stronger than the electrostatic attraction between 1+ and 1- ions so therefore more energy is needed ro overcome the bonds in a 2+ substance than a 1+ substance
What two things must happen to allow a substance to dissolve
The ionic lattice has to break down Water molecules must be attracted to the ions and surround them
Explain the difference in the attraction between Na+ ions and water and Cl- ions and water
Na+ ions are attracted to the partial negative side of water which is the oxygen side Cl- is attracted to the partial positive side of water which is the hydrogen side
Substances with higher melting points are ________ to dissolve than substances with lower melting points because they have _________ forces of attraction which are __________ to overcome to break the ionic lattice
Harder Stronger Harder
What must happen for a ionic substances to conduct electricity?
There have to be ions that are free to move
Why don’t solid ionic substances conduct electricity?
Because they have no ions which are free to move so they have no mobile charge carriers
Define covalent bonding
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Define dative covalent bonding
A type of covalent bonding where both electrons in the shared pair are donated by one atom
Explain the bonding of NH4 +
The NH3 molecules can donate the lone pair to a hydrogen ion that has no electrons but needs 2 in its outer shell so the N donates both of the electron for the NH bond
Define average bond enthalpy
The energy required to break one mole of a specified type of bond in a gaseous molecule
Average bond enthalpy is a measurement of the ____________ of a covalent bond. The larger the bond enthalpy, the ———- the bond.
Strength Stronger
The shape of the molecules or ions is determined by the number of __________ ______ on the central atom.
Electron pairs
Why do electron pairs make different shapes?
Electron pairs repel each other as far as possible and lone pairs repel more than bonded pairs as they sit closer to the nucleus
Describe the steps to work out the shape of a molecule
Draw a dot and cross diagram for the molecule or ion Count the number of pairs of electrons on the outer shell of the central atom. The number of pairs of electrons will give you the basic shape Count how many of the pairs of electrons are bonding pairs and how many are lone pairs. This will give the final shape and bonding angles
How many pairs of bonded electrons or electron regions are in CO2
2 bonded regions
What is the shape of a CO2 molecule
Linear
What is the bonding angle in CO2?
180
What is the bonding angle in a linear molecule
180
How many bonded pairs and how many lone regions are there in BF3?
3 bonded No lone regions
What is the shape of BF3 molecules?
Trigonal planar
What are the angles in a trigonal planar molecule?
120
How many pairs of bonded electrons are there and how many lone pairs are there in CH4?
4 bonded No lone
What is the shape of CH4?
Tetrahedral
What are the angles in a tetrahedral molecule?
109.5
How many bonded pairs and how many lone pairs are there in SF6?
6 bonded No lone
What is the shape of SF6?
Octahedral
What is the bonding angle in a octahedral molecule?
90
How many bonded pairs and lone pairs are there in NH3?
3 bonded 1 lone
What is the shape of NH3?
Trigonal pyramidal
What is the bonding angle in a trigonal pyramidal molecule?
120
How many bonded pairs and lone pairs are there in H20?
2 bonded 2 lone
What is the shape of a H20 molecule?
Non linear
What are the angles in a non linear molecule?
104.5
Define oxidation number
A measure of the number of electrons that an atom uses to bond with atoms of another element
What is the oxidation number of F?
-1
What is the oxidation number of O when with fluorine?
+2
What is the oxidation number of oxygen when in a peroxide?
-1
What is the oxidation number of oxygen normally?
-2
What is the oxidation number of a group one atom?
+1
What is the oxidation number of a group 2 atom?
+2
What is the oxidation number of a group 7 atom?
-1
Do we know the oxidation numbers of group 3,4,5,6,0 atoms
No
The sum of the oxidation numbers should be _______ to the charge on the _________ or ______
Equal Compound or ion
Is the sign written before or after the charge on an oxidation number?
Before
What would be the oxidation number on copper (I)?
+1
What is the oxidation number of a s atom in a sulphate ion?
+6
What is the oxidation number of a nitrogen atom in a nitrate ion?
+5
What is the oxidation number a chlorine atom on a chlorate (III) ion?
+3
What is the formula on a chlorate (III) ion?
ClO3
Define a redox reaction
A reaction in which oxidation and reduction happen at the same time
What does oxidation mean in terms of electrons?
Oxidation is the loss of electrons
What does reduction mean in terms of electrons and oxidation number?
Reduction means an increase in oxidation number and the gain of electrons
Define electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond
Explain the pauling scale in electronegativity
As you go up the (halogens reactivity direction) the electronegativity increases As you fo right from the metal side the electronegativity increases
When the electronegativity difference is higher than ____ the bonding is _________ and if the difference is lower then the bonding is _________
1.7 Ionic Covalent
How does a polar bond form
A polar bond forms when 2 atoms of differing electronegativity are bonded covalently
Explain the polar bonding between hydrogen and fluorine
As fluorine has a higher electronegativity the electrons will be more attracted to hydrogen than fluorine meaning that the fluorine atom will have a partial negative charge and the hydrogen atom will have a partial positive charge and the molecule is said to be a dipole and a polar bond
whether or not a molecule is polar depends on…..
whether the bonds are polar and the shape of the molecule
For a molecule to be polar the molecule required ———- bonds with ———— that do not ———- —— due to their direction
polar dipoles cancel out
Are symmetrical molecules non-polar or polar, why?
nonpolar because the dipoles in the molecule will cancel out due to their direction
Define intermolecular forces
The forces of attraction between molecules which have covalent bonds
What are the 3 main types of intermolecular forces?
Induced dipole dipole interactions - london forces Permanent dipole dipole interactions Hydrogen bonding
How strong are london forces?
The weakest type of intermolecular force
Do london forces exist between non polar forces, polar forces or both?
Both irrespective of whether they are polar or not
What do london forces act between?
Induced dipoles
Explain how london forces form
An instantaneous dipole will form due to fluctuations in electron density. This then induces a dipole on an adjacent molecule. This induced dipole will then induce a dipole on another molecule and london forces are made between the 2 induced dipoles
Are induced dipoles temporary or permanent?
Temporary
What affects the strength of the london forces between dipoles? Why?
More electrons in an atom or molecule Because more electrons produce larger instantaneous and induced dipole so the induced dipole dipole attractions will be greater so the forces of attraction between the molecule will be stronger and this will mean that the boiling and melting points will be higher
Which noble gas has the highest boiling point? Argon Neon Helium
Argon
What do permanent dipole dipole interactions form between
Polar molecules
In the solid state, simple molecules will exist in a ——— ——— lattice: The molecules are held together by ——— ————— forces ( the type depends on the molecule) The atoms within the molecule are held together by ———— —————- bonds
Simple molecular Weak intermolecular Strong covalent
Why are melting points between simple molecular lattices weak?
Only the weak intermolecular forces need to be overcome to make it a liquid so the energy required is low
Are non polar substances soluble in non polar solvents or polar solvents?
Non polar because the molecules form weak london forces with the molecules of the solvents and this weakens the intermolecular forces in the lattice and the substance disolves
Some polar substances will dissolve in ———- solvents
Polar
Are simple molecular substances conductors of electricity?
No because there are no mobile charge carriers
What does hydrogen bonding occur between ?
An electronegative atom which has a lone pair of electrons eg NOF And a H atom attached to an electronegative atom
What are the 3 atoms that form hydrogen bonds?
O N F
Why is ice less dense than water?
The hydrogen bonds push the water molecules into a tetrahedral shape which takes up more space and this means it is less dense
Why does water have high melting and boiling points?
The hydrogen bonds between then need more energy to overcome them and therefore both the melting point and boiling points are higher than expected
Define oxidation number
A measure of the number of electrons that an atom uses to bond with atoms of another
What is the oxidation number of an unreacted element
0
What is the oxidation number of fluorine?
-1
What is the oxidation number of oxygen
-2 or -1 if there is a peroxide +2 if bonded to fluorine
Group 1 oxidation number
+1
Group 2 oxidation number
+2
Oxidation number of group 7 atoms
-1
Are the oxidation numbers indicated by roman numerals
Yes
What is the oxidation number of sulphur in a sulphate ion?
+6
What is the oxidation number of nitrogen in a nitrate ion?
+5
Define redox
A reaction in which oxidation and reduction happen at the same time
Oxidation is
Loss of electrons
Reduction is
Gain of electrons
