Chapter 2.2- Electrons,Bonding and structure Flashcards
How many electrons can each shell hold?
2n^2 number of electrons where n=shell number
What does n represent?
the principle quantum number (indicates the shell number)
How many electrons does the 1st shell contain?
2 (1)^2=2
How many electrons does the 2nd shell contain?
8
How many electrons does the 3rd shell contain?
18
How many electrons does the 4th shell contain?
32
What is a shell?
group of atomic orbitals with the same principle quantum number, n. Also known as the main energy level.
What model did Niels Bohr dissprove?
plum-pudding model, which proposed that electrons were found within a a sea of positive charge.
What was Bohr’s proposed model for the structure of the atom?
his model depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits (defined by their energy levels) around the centre.
What is an orbital?
a region around the nucleus that can hold up to two electrons, with opposite spins
What are the four different types of orbital?
s , p, d, f
What is the shape of an s-orbital?
spherical shape
From n=1, how many s-orbital are found in each shell?
1
What is the shape of the p-orbitals?
3D dumb-bell shape
From n=2, how many p-orbitals are found in each shell?
three p-orbitals, px, py and pz
From n=3 upwards, how many d-orbitals are found in each shell?
5
From n=4 upwards, how many f orbitals are found in each shell?
7
How many electrons can be held in each of the p orbitals in total?
6
How many electrons can be held in each of the s-orbitals in total?
2
How many electrons can be held in each of the d-orbtials in total?
10
How many electrons can be held in each of the f-orbitals in total?
14
What are orbitals that are in the same energy level grouped together called?
sub-shells
How are each orbitals represented?
boxes
How are electrons arranged in each box (orbital)
- electrons have a property called spin
- the two electrons in each box (orbital) must have opposite spins
Within a shell, what are the sub-shells in increasing energy?
s, p, d, f
What is the name of the principle of how to work out the electron configuration of at element?
Aufbau principle
What are the three rules for electron configuration regarding the electrons in the shells of an atom?
- electrons are added, one at a time, to ‘build up’ the atom
- the lowest available energy level is filled first. You can consider this level as being the closest to the nucleus.
What are the two rules for electron configuration regarding the sub-shells
- when a sub-shell is built up with electrons, each orbital is filled singly before pairing starts
- the 4s orbital is at a slightly lower energy level than the 3d orbital. This means 4s will fill before 3d.
What is the ‘last in, first out’ principle for electron configuration?
Electrons in the highest energy level are the first to be lost
What is the electron configuration of krypton?
1s^2, 2s^2 2p^6, 3s^2 3p^6, 4s^2 3d^10 4p^6
What is the electron configuration of Zn^2+?
1s^2, 2s^2 2p^6, 3s^2 3p^6 3d^10
When an atom becomes a positive ion, does the 4s or 3d sub shell empty first?
4s
What is the electron configuration of Cr?
- 1s^2, 2s^2 2p^6, 3s^2 3p^6, 4s^1 3d^5
- the 4s sub-shell isn’t full up because when the electron is added to the 3d sub-shell instead the ion is thought to be more energetically stable
What are the three types of chemical bond?
- ionic
- covalent
- metallic
What is an ionic bond?
electrostatic attraction between positive and negative ions
Why do elements have a tendency to bond?
To achieve a noble gas configuration which is energetically stable
What are dot-and-cross diagrams?
- used to show the origin of electrons in chemical bonding
- dots are used to represent the electrons in one element, and crosses are used to represent the electrons in another element
Why do ionic structures form giant ionic lattices?
- each ion is surrounded by oppositely charged ions
- these ions attract each other from all directions, forming a 3D giant ionic lattice
Name an example of an ionic compound that forms a giant ionic lattice
- NaCl (sodium chloride)
- Each Na+ is surrounded by six Cl-
- Each Cl- is surrounded by six Na+
Why do ionic compound have a high melting and boiling point?
- they are solid at room temperature
- a large amount of energy is needed to break the strong electrostatic bonds that hold the oppositely charged ions together
Why is the melting point of MgO higher than the melting point of NaCl?
- the charges on the Mg^2+ and O^2- ions are greater than those on Na^+ and Cl^-.
- greater the charge, the stronger electrostatic forces between the ions.
Does a solid ionic lattice conduct electricity?
- no
- the ions are held in fixed positions and no ions can move
When does an ionic compound conduct electricity?
- when it is melted or dissolved in water
- the solid ionic lattice breaks down and the ions are free to move
Are ionic lattices soluble?
-yes in polar solvents (contains polar bonds)
What is a polar bond?
atoms that do not share electrons equally, and it results in the atoms having very small charges on them
Name a polar molecule
- water (H20)
- delta + on H atoms
- delta - on O atoms
How do polar water molecules break down an ionic lattice?
- the slight charges within the polar molecule are able to attract the charged ions in the giant ionic lattice
- the lattice is therefore disrupted and the ions are pulled out of it
What does soluble mean?
able to be dissolved, especially in water
What is a covalent bond?
strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What is a single covalent bond and name two examples of compounds which have single covalent bonds?
- covalent bond involves one shared pair of electrons
- Chlorine (Cl2) water(H2O)
What is a multiple covalent bond and name two examples of compounds which have multiple covalent bonds?
- covalent bond which involves more than one shared pair of electrons
- oxygen( 02) contains 2 shared pair of electrons(double bond)
- Nitrogen (N2) contains 3 shared pair of electrons (triple bond)
What is a dative covalent bond (coordinate bond)?
one atom donates both of the electrons in the covalent bond
What is used to represent a dative covalent bond?
arrow
What is an example of a compound which has dative covalent bond?
ammonia (NH4)
What are the two different structures of covalent bonding?
- simple molecular lattice
- giant covalent lattice
What are simple molecular lattices?
-made up of small molecules
-within each molecule, the atoms are tightly held together by covalent bonds
-between the molecules, weak intermolecular forces of attraction are present
-
Are the boiling/melting point of simple molecular substances high or high and why?
- have a low melting and boiling point
- the weak intermolecular forces of attraction between the molecules requires a small amount of energy to disrupt these forces
Are simple molecular substances soluble?
- yes in non-polar solvents
- ‘like dissolves like’: weak intermolecular forces between the molecules of the non-polar solvent are similar to that in simple molecular substances
Are simple molecular substances able to conduct electricity?
- no
- no charged particles are free to move and carry charge
What are giant covalent structures?
- atoms are joined to adjacent atoms by strong covalent bonds
- lots of strong covalent bonds throughout the structure
What are two examples of giant covalent structures?
- diamond
- graphite
- SiO2
Do giant covalent structures have low or high melting/boiling points and why?
- high melting and boiling point
- high temperatures are needed to break the strong covalent bonds within the lattice
Are giant covalent structures able to conduct electricity?
-non-conductors of electricity became there are no free charged particles, except for graphite
Are giant covalent structures soluble?
-not soluble in both polar and non-polar solvents because the covalent bonds in the lattice are too strong to be broken by either polar or non-polar solvents
What is a lone pair?
outer shell pair of electrons that are not involved in chemical bonding
Name two substances that have lone pairs
- water(H2O0
- ammonia (NH3)
What is the average bond enthalpy?
- energy required to break a bond
- covalent bonds are not all the same strength, so some are easier to break and some are harder
In order to achieve a noble gas configuration, how many covalent bonds do elements make?
-the number of bonds an element forms corresponds to the number of electrons they need in order to obtain a noble gas configuration
How many covalent bonds does carbon, nitrogen, oxygen and hydrogen make?
- carbon 4
- nitrogen 3
- oxygen 2
- hydrogen 1
What is an oxonium ion?
- H30+
- Formed when an acid is added to water
- HCl(g) + H20(l)- —-H30+(aq) + Cl-(aq)
- one of the lone pairs around the oxygen atom provides the bonding electrons to form a dative covalent bond
What atoms in group 15 can expand their octet?
- P
- As
What elements in group 16 can expand their octet?
- S
- Se
- Te
What elements in group 17 can expand their octet?
- Cl
- Br
- I
- At
What is the octet rule?
elements tend to combine in such a way that each atom has eight electrons in its outer shell
What is a better rule that the octet rule?
- unpaired electrons pair up
- the maximum number of electrons that can pair up is equivalent to the number of electrons in the outer shell
What are the two things that dictate the shape of a compound or ion?
- number of electron pairs around the central atom
- the nature of these pairs: bonding pairs or lone pairs
What is the name of the shape of a molecule which has 1 bonded electron pair around the central atom and give an example?
- linear
- H2
What is the name of the shape of a molecule which has 2 bonded electron pairs around the central atom and give an example?
- linear
- CO2
What is the name of the shape of a molecule which has 3 bonded electron pairs around the central atom and give an example?
- trigonal planar
- BF3
What is the name of the shape of a molecule which has 4 bonded electron pairs around the central atom and give an example?
- tetrahedral
- CH4
What is the name of the shape of a molecule which has 5 bonded electron pairs around the central atom and give an example?
- trigonal bipyramid
- PCl5
What is the name of the shape of a molecule which has 6 bonded electron pairs around the central atom and give an example?
- octahedral
- SF6
What is the bond angle in a linear molecule, 2 bonding pairs?
180 degrees
What is the bond angle in a trigonal planar molecule, 3 bonding pairs?
120 degrees
What is the bond angle in a tetrahedral molecule, 4 bonding pairs?
109.5 degrees
What is the bond angle/s in a trigonal bipyramid molecule, 5 bonding pairs?
90 and 120 degrees
What is the bond angle in a octahedral molecule, 6 bonding pairs?
90 degrees
How do molecules with lone pairs affect the bonding angles off a molecule?
- a lone pair of electrons is slightly more electron dense than a bonded pair.
- a lone pair repels more than a bonded pair. Each lone pair reduces the bond angle by about 2.5 degrees
What shape and bond angle is an methane molecule?
- tetrahedral
- 109.5 degrees
What shape and bond angle is an a ammonia molecule?
- pyramidal
- 107 degrees (3 bonding pairs and 1 lone pair)
What shape and bond angle is a water molecule?
- non-linear
- 104.5 degrees (2 bonding pairs and 2 lone pairs)
What is meant by the term electronegativity?
ability of an atom to attract the bonding electrons in a covalent bond
In the periodic table, what is the trend in electronegativity?
increases towards fluorine, from all directions (left to right across each period and up each group)
What is a polar bond?
- if the two bonding atoms in a covalent bond are different, their attraction for the shared pair of electrons is unequal
- this results in a small charge difference across a bond, creating a permanent dipole
What is a polar molecule?
- a molecule that contains polar bonds
- the molecule must be non-symmetrical so the dipoles don’t cancel out
Is water a polar molecule?
- yes
- oxygen is more electronegative than hydrogen and there is an overall dipole because the molecule is not symmetrical
Is carbon dioxide a polar molecule?
- no
- oxygen has polar bonds, but there is no overall dipole because the molecule is symmetrical.
What are the three main types of intermolecular forces?
- London forces
- permanent dipoles
- hydrogen bonds
What are London (dispersion) forces of attraction?
-caused by the constant random movement of electrons in atoms shells.
-at any moment, there will be an instantaneous (temporary) dipole across the molecule
-this induces a dipole in neighbouring molecules, which in turn induces further dipoles on their neighbouring molecules
-
What are permanent dipole-permanent dipole interactions?
-if correctly alligned, two molecules which have permanent dipoles will be attracted to one another
What are permanent dipole-induced dipole interactions?
- when molecules which have permanent dipoles are near neutral molecules that are non-polar, it is able to cause electrons in the shells nearby molecule to shift slightly
- non-polar molecule becomes slightly polar and then an attraction occurs
- known as permanent dipole-induced dipole interaction
What is the name given to describe permanent dipole-induced dipole interactions, permanent dipole-permanent dipole interactions and London forces?
van der Waals forces
What does intermolecular forces mean?1
forces between molecules
What determines the strength of London Forces?
- the number of electrons
- greater the number of electrons, the stronger the forces as the induced dipoles are larger
What are hydrogen bonds?
- strong permanent dipole-permanent dipole forces of attraction
- between an electron deficient Hydrogen atom (O-H delta +, N-H delta + or F-H delta + on one molecule and a lone pair of electrons on a highly electronegative atom (O,N of F) on a different atom
Why is ice less dense than water as a result of hydrogen bonding?
- when ice forms, water molecules arrange themselves into an orderly pattern and hydrogen bonds form between the molecules
- ice has an open lattice with hydrogen bonds holding the water molecules far apart
Why does water have such a high melting/boiling point?
- hydrogen bonds are much stronger than other intermolecular forces
- these strong forces must be overcome
What are two more unique properties of water that have arisen due to hydrogen bonds?
- high surface tension
- viscosity of water is high
Rank ionic/covalent bonds, hydrogen bonds, permanent dipole-dipole and other dipole forces and London Dispersion forces in order of relative strength?
weakest to strongest
- London forces
- permanent dipole-dipole forces
- hydrogen bonds
- ionic/covalent bonds
