module 2: foundations in chemistry Flashcards
which subatomic particles are found in the nucleus?
protons and neutrons
where are electrons found in an atom?
arranged in shells surrounding the nucleus
what is the relative mass of an electron?
1/1836
what are isotopes?
atoms with the same number of protons and electrons, but with different numbers of neutrons
what is the mass number of an atom?
the number of protons and neutrons
what is the atomic number of an atom?
the number of protons
what is an ion?
a charged atom
what are cations?
positive ions
what are anions?
negative ions
how are ions formed?
when an atom gains or loses electrons
what is meant by the relative atomic mass?
the weighted mean mass of an atom of an element, relative to 1/12th of the mean mass of an atom of carbon-12
what is meant by the relative isotopic mass?
the mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12
what is meant by the relative molecular mass?
the weighted mean mass of a molecule of a compound compared with 1/12th of the mass of an atom of carbon-12
state the similarities and differences between isotopes of the same element
similarities:
- same number of protons
- same number of electrons
differences:
- different number of neutrons
- different mass numbers
why do isotopes have the same chemical properties?
they have the same number of electrons in the outer shell
when does ionic bonding occur?
between a metal and a non-metal
what is the charge on a carbonate ion?
2-
what is the charge on a sulfate ion?
2-
what is the empirical fomula?
the simplest whole number ratio of atoms of each element present in a compound
what is the molecular formula?
shows the number and types of atoms of each element present in a molecule
what is a standard solution?
a solution of known concentration
what is the limiting reagent?
the reactant that is not in excess, which will be used up first and stop the reaction
what is the ideal gas equation?
pV = nRT
what is an acid?
a species that releases H+ ions in aqueous solutions
what is an alkali?
a type of base that dissolves in water forming hydroxide ions
what is a strong acid?
an acid which fully dissociates in aqueous solutions
what is a weak acid?
an acid which partially dissociates in aqueous solutions
what is oxidation?
the loss of electrons
what is reduction?
the gaining of electrons
what is the effect of oxidation and reduction on the oxidation number?
oxidation - increase in oxidation number
reduction - decrease in oxidation number
what is an oxidising agent?
a reagent that accepts electrons from another species
what is disproportionation?
a redox reaction in which the same element is both oxidised and reduced
what is the formula for the maximum number of electrons a shell number n?
maximum number of electrons = 2n²
what is an atomic orbital?
a region around the nucleus that can hold up to two electrons, with opposite spins
what is a shell?
a group of atomic orbitals with the same principal quantum number
what is the principal quantum number?
a number representing the relative overall energy of each orbital
what are the four different types of orbitals?
- s-orbitals
- p-orbitals
- d-orbitals
- f-orbitals
what is the shape of a s-orbital?
spherical
what is the shape of a p-orbital?
dumbell
what is the maximum number of electrons that can fill a s-subshell?
2 electrons
what is the maximum number of electrons that can fill a p-subshell?
6 electrons
what is the maximum number of electrons that can fill a d-subshell?
10 electrons
how many orbitals does a s-subshell have?
1
how many orbitals does a p-subshell have?
3
how many orbitals does a d-subshell have?
5
what are the rules by which electrons are arranged in shells?
- electrons are added one at a time
- lowest available energy level is filled first
- each energy level must be filled before the next one can fill
- each orbital is filled singly before pairing
- 4s is filled before 3d
why does the 4s orbital fill before the 3d orbital?
the 4s orbital has lower energy than the 3d orbital, before it is filled
why does each orbital fill singly before pairing?
- electrons with the same spin repel each other (spin-pair repulsion)
- therefore, electrons will occupy separate orbitals in the same subshell first to minimise this repulsion and have their spin in the same direction
what is ionic bonding?
the electrostatic attraction between positive and negative ions
what are sub-shells?
a group of orbitals of the same type within a shell
explain why ionic compounds have high melting and boiling points
describe the relative energies of the 2s orbital and each of the three 2p orbitals in a nitrogen atom
- p-orbitals have greater energy than s-orbitals
- p-orbitals have equal energy
what is covalent bonding?
the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
what is a covalent bond?
a shared pair of electrons
where does covalent bonding occur?
between non-metals
what is the shape and bond angle of a molecule with 4 bonded pairs and 0 lone pairs?
tetrahedral, 109.5°
what is the shape and bond angle of a molecule with 3 bonded pairs and 1 lone pair?
pyramidal, 107°
what is the shape and bond angle of a molecule with 2 bonded pairs and 2 lone pairs?
non-linear, 104.5°
what is the shape and bond angle of a molecule with 3 bonding regions and 0 lone pairs?
trigonal planar, 120°
what is the shape and bond angle of a molecule with 2 bonding regions and 0 lone pairs?
linear, 180°
what is electronegativity?
a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
what is a dative covalent bond?
a shared pair of electrons in which the bonded pair has been provided by one of the bonded atoms only, also called a coordinate bond
what is the most electronegative atom?
fluorine
what is the trend of electronegativity across a period of the periodic table?
electronegativity increases across a period of the periodic table
what is the trend of electronegativity up a group of the periodic table?
electronegativity increases going up a group of the periodic table
what is the trend of nuclear charge and atomic radius going across the periodic table?
- nuclear charge increases
- atomic radius decreases
what is the electronegativity difference between atoms in a covalent bond?
0
what is a non-polar bond?
a type of covalent bond where the bonded electron pair is shared equally between the bonded atoms
when will a bond be non-polar?
- when the bonded atoms are the same, or
- the bonded atoms have the same or similar electronegativity
why are hydrocarbons non-polar?
carbon and hydrogen atoms have very similar electronegativities, so form non-polar bonds
what is a polar bond?
a type of covalent bond where the bonded electron pair is shared unequally between the bonded atoms
when will a bond be polar?
- the bonded atoms are different, and
- have different electronegativity values
what is a dipole?
a separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge δ+ and the other has a small negative charge δ−
what is a permanent dipole?
a small charge difference that does not change across a bond, with δ+ and δ− partial charges on the bonded atoms
what are the three main categories of intermolecular forces?
- induced dipole-dipole interactions (london forces)
- permanent dipole-dipole interactions
- hydrogen bonding
what are intermolecular forces?
weak interactions between dipoles of different molecules
in which type of molecules do you find london forces?
all molecules, whether polar or non-polar
explain how induced dipoles are created
- movement of electrons produces a changing dipole in a molecule
- at any instant, an instantaneous dipole will exist, but its position is constantly changing
- the instantaneous dipole induces a dipole on a neighbouring molecule
- the induced dipole induces further dipoles on neighbouring molecules, which then attract one another
how does the number of electrons affect the strength of induced dipole-dipole interactions?
the more electrons in each molecule:
- the larger the instantaneous and induced dipoles
- the greater the induced dipole-dipole interactions
- the stronger the attractive forces between molecules
what is an ionic lattice?
a repeating pattern of oppositely charged ions
state and explain two anomalous properties of ice caused by hydrogen bonding
- ice is less dense than water because the molecules in ice are held apart in an open lattice structure by hydrogen bonds
- ice has a relatively high melting point because hydrogen bonds are relatively strong