Atoms are made up of Protons, Neutrons and Electro
- Made up of Protons, Neutrons and Electrons
Electrons have -1 charge - move around the nucleus in orbitals
Nucleus made up of Protons and Neutrons
Mass and Charge of these Subatomic Particles are very small, so relative mass and relative charge are used instead.
Nuclear Symbols show numbers of Subatomic Particle
Mass Number (A) - the total number of Protons and Neutrons in the nucleus
Atomic (Proton) Number (Z) - number of protons in the nucleus - identifies the element
ALL atoms of the same element have the same number of protons
For neutral atoms with no overall charge, the number of electrons is the same as the number of protons.
Number of neutrons - A minus Z
Ions Have Different Numbers of Protons and Electro
Negative ions have more electrons than protons
Br- The negative charge means there's 1 more electron than there are protons.
Br has 35 protons, so Br- must have 36 electrons.
The overall charge = 35 - 36 = -1
Positive Ions have fewer electrons than protons
Mg2+ The 2+ charge means there's 2 fewer electrons than there are protons
Mg has 12 protons so Mg2+ must have 10 electrons
The overall charge = 12 - 10 = 2+
IIsotopes of an element are atoms with the same nu
Different mass numbers mean different numbers of neutrons
The atomic numbers are the same - Both isotopes have 17 protons and 17 electrons
Number and arrangement of electrons decides the chemical properties of an element - Isotopes have the same configuration of electrons so have the same chemical properties
Isotopes have slightly different physical properties - different densities, rates of diffusion etc.
Physical properties depend more on the mass.
Relative Masses - Masses of Atoms compared to Carb
Relative atomic mass, Ar: The weighted mean mass of an atom of an element compared to one twelfth of the mass of an atom of carbon-12: an average of the isotopes of the element, so not usually a whole number
Relative isotopic mass: The mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12: Always a whole number
Formula mass: The weighted mean mass of a formula unit compared to one twelfth of the mass of an atom of carbon-12: Used for compounds that are ionic or giant covalent - add up all the Ar of all the ions
Relative molecular mass, Mr: The weighted mean mass of a molecule compared to one twelfth of the mass of an atom of carbon-12: Add up all the Ar of all the atoms in the molecule