Ch 2 Lecture Notes for Friday September 18 2 1b Atomic Number Mass Number and Atomic Symbols o All atoms in a given element have the same number of protons this accounts for the nuclear charge combined Protons are denotes by the symbol Z o Mass number is denoted by the symbol A it is the number of protons and neutrons Atoms of an element with different number of neutrons are called isotopes Example Carbon 12 has six protons and six neutrons Carbon 13 has six protons and seven neutrons o Atomic Symbol either 1 or 2 letter symbol designated to represent an element o Atomic weight or atomic mass the avg mass of each isotope of an element with reverence to the overall abundance of the isotopes Atomic mass relative abundance of isoptope 1 100 x atomic mass of isotope 1 repeat for isotope 2 and so on Every isotope has its own relative abundance Ionic bonding o In ionic bonding ions are held by electrostatic attraction includes the complete transfer of valence electrons forming two oppositely charged ions o Ionic bonds have cations positively charged and written first and anions negatively charged and written second o Cation formed when electrons are lost o Anion formed when electrons are gained Electrostatic Forces and Coulomb s Law o as ion charges increase force of attraction increases Example there is a greater force of attraction between 2 ions and 2 ions than there is in 1 and 1 ions o as distance between ions increases force of attraction decreases o side note the stronger the ionic bonding the higher the melting point Covalent bonding o when atoms are held together by shared electrons
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