Chapter 2 Atoms, ions and compounds Flashcards
Isotopes
- Same number of protons and electrons
- Atoms of the same element with different number of neutrons and different masses
- Most elements are made up of a mixture of isotopes
Atomic structure
- Protons
- Neutrons
- Electrons
Mass of protons, neutrons and electrons
- Protons and neutrons have the same relative mass of 1
- Electrons have a negligible mass
Overall charge of an atom
The charges of the protons and electrons cancel out -> atom is neutral (no overall charge)
Ratio of number of protons: number of neutrons in an atom
same
Atomic number
Number of protons
Mass number
Number of protons + number of neutrons
Isotopes and chemical reactions
- Different isotopes of the same element have the same number of electrons
- Number of neutrons has no effect on reactions of an element -> different isotopes of an element react in the same way
Isotopes and physical reactions
Higher mass isotopes of an element have a higher melting point, boiling point and density
Ion
- Charged atom
- Number of electrons is different from the number of protons
Cations
- Positive ions
- Less electrons than protons
Anions
- Negative ions
- More electrons than protons
What predicts chemical reactions
Number of electrons
Mass of a carbon-12 isotope
12 atomic mass units (12u)
The standard mass for atomic mass
1u, the mass of 1/12th of an atom of carbon-12
- 1u = mass of a proton or a neutron
Relative isotopic mass
The mass of an isotope relative to 1/12th of the mass of an atom of carbon-12
Relative atomi mass (Ar)
Weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12
The weighted mean mass takes account of:
- % abundance of each isotope
- the relative isotopic mass of each isotope
Mass spectrometer
to find % abundance of the isotopes in a sample of an element experimentally
Process of a mass spectrometer
- A sample is placed in the mass spectrometer
- The sample is vaporised
- The sample is ionised (to give each particle a positive charge)
- Ions are accelerated
- Ions are deflected (size of deflection depends on the mass so heavier isotopes are deflected less than lighter ones)
- The ions are detected as an m/z
- Each ion reaching the detector adds to the signal, so the greater the abundance, the larger the signal
m/z full form
mass:charge ratio
Equation of m/z
m = relative mass of ion
z = relative charge on ion
Axis on the graph of m/z
x-axis: m/z
y-axis: % abundance
Binary compounds
Contains 2 elements only
Binary compounds
- Name of 1st element + add -ide to second element
- for ionic compounds, metal ion comes first
Polyatomic ions
An ion contain atoms of more than one element bonded together
Writing formulae from ions
- The overall charge is zero so the ionic charges must balance
- sum of positive charges = sum of negative charges
Diatomic molecules
contain 2 atoms bonded together
State symbols
(g) - gas
(l) - liquid
(s) - solid
(aq) - dissolved in water (aqueous)
Do ions have the same mass number or different mass number?
Same mass number
