W3 From atoms to molecules ll Flashcards
What is an atomic orbital?
Atomic orbitals can hold two electrons (of opp spins) and is described as a 3D region within which there is a 95% probability of finding the electrons.
What is the principal quantum number?
Principle quantum number n. n=1 the lowest-energy shell closest to the nucleus.
How many subshells are there?
4 subshells (s,p,d,f)
How many orbitals in an S, P, D and F sub shell
S=1 orbital
P= 3 orbitals
d= 5 orbitals
F= 7 orbitals
An orbital can hold how many electrons?
2
A shell can hold up to how many electrons?
Each shell can contain up to 2n^2 electrons, where n is the number of the shell.
What are valence electrons and what does valence mean?
Outermost electrons
Valence= electrons an atom must lose or gain to attain the nearest noblest noble gas.
E.g. C has 4 valence electrons (config:1s2 2s2 2p2) it needs 4 e- to become …. 2p6, so valence is 4
What is the Aufbau Principle?
Orbitals and shells fill in order of increasing energy. 1s shell lower in energy than a 2s shell, which is lower in energy than a 3s shell.
Atomic orbitals in the same shell = s atomic orbital is lower in energy than p and p is lower in energy than d.
What is the Pauli exclusion principle?
each atomic orbitals can hold a maximum of 2 electrons having opposite spin
What is Hund’s rule?
When there are two or more orbitals of the same energy (degenerative orbitals), electrons go into different orbitals rather than pair up in the same orbital.
What is the Octet rule?
A filled shell of electrons is especially stable
Atoms transfer or share electrons to attain a filled shell of electrons (noble gases)
8 valence electrons for the elements in the second row (Octet Rule)
Elements in the third and higher rows can have an “expanded octet” e.g. Al, Si, P, S, Cl
What does each sub shell contain?
One or more atomic orbital. Exact orientation of an
orbital in the space (px, py or pz). Identified by the magnetic quantum number ml
How many electrons in:
shell 3?
shell 4?
=18 (3S 3P 3P 3P FIVE 3D)
=32 (4S 4P 4P FIVE 4D SEVEN 4F)
Ground-state electronic configuration: How can we determine it? (3)
- Aufbau principle
- Pauli exclusion principle
- Hund’s rule
What occurs in a nonpolar covalent bond?
Electrons are shared equally
What is a Polar covalent bond?
Unequally shared pair of bonding electrons
What is the definition of Electronegativity?
Which atom attracts the shared electrons in a diatomic molecule?
Power of an atom in a molecule to attract electrons to itself.
The more electronegative atom.
Pauling electronegativity values:
When are Ionic bonds formed?
When are covalent bonds formed?
Ionic bonds form when electronegativity
difference between 2 atoms is > 1.7
Covalent bonds form when electronegativity
difference between 2 atoms is < 1.7
What is meant by intermolecular forces?
Attraction forces between molecules (non-bonding interactions)
3 types of intermolecular forces:
1) Dipole-dipole interactions
2) Van der Waals Forces
3) Hydrogen bonding
Dipole-dipole interactions
Interactions between the positive end of one
dipole and the negative end of another dipole
Van der Waals Forces:
Relatively weak forces of attraction that exist
between nonpolar molecules. Distance-dependent interactions. Called induced dipole–induced dipole interactions
Hydrogen bonding
- Attractive force between the H attached to an
electronegative atom of one molecule and an electronegative atom of the same
(intramolecular) or a different molecule (intermolecular). i.e. H2O - NOF Elements
What is the lewis structure?
Each valence electron is symbolised by a dot
A bonding pair of electrons is symbolised by a pair of dots or by a dash ( -)
Sharing of one pair of electrons - single bond
Sharing of two/three pairs of electrons - double/ triple bond
What typical elements have lone pairs?
Oxygen atoms, nitrogen atoms, and the halogens
(F, Cl, Br, I)
What is sp3 hybridisation?
What is the shape?
Bond angle?
-Used when C forms 4 single bonds, all blended
-4 sp3 orbitals of equal E
-Tetrahedral
-Bond angles 109.5°
What is sp2 hybridisation?
What is the shape?
Bond angle?
-Used when C forms a double bond, 2s plus 2 2p blended, 3 sp2
-Orbitals of equal E + 1p orbital
-Trigonal geometry
-Bond angles 120°
What is sp hybridisation?
What is the shape?
Bond angle?
-Used when C forms a triple bond or a cumulate Double bond, 2s plus 1 2p blended, 2 sp orbitals of equal E + 2p orbital
-Linear geometry
-Bond Angles 180 °
