Valence Electrons & Bohr Diagrams

Atomic Structure Atoms have a nucleus that contains Protons and Neutrons Electrons are contained in shells that surround the nucleus An atom is made of mostly empty space Protons have a positive charge Electrons have a negative charge Neutrons are Neutral

Valence Electrons Electron Shell Number of Electrons 1 2 8 3 4 18 5 6 Each electron shell can hold a certain number of electrons Electron shells are filled from the inside out Noble Gases have full outer electron shells All other elements have partially filled outer electron shells Electron Shell Number of Electrons 1 2 8 3 4 18 5 6 32 7

Valence Electrons The electrons in the outer most electron shell are called valence electrons The shell containing electrons that is furthest from the nucleus is called the valence shell The number of electron shells with electrons is the same as the period number

Noble Gas Stability Noble gases are usually unreactive This is because they have full valence shells An element with a full valence shell is a happy element  For two atoms to join together atoms must gain, lose or share electrons Elements with full valence shells do not easily gain or lose electrons

Noble Gas Stability Atoms want to gain stability Atoms will try to gain or lose electrons to have a full valence shell Metals try to lose electrons Non-Metals try to gain electrons

Becoming An Ion Electrons are negatively charged Protons are positively charged Neutral atoms do not have a charge because the number of protons is the same as the number of electrons When atoms gain or lose electrons they become positively or negatively charged An atom with a charge is called an Ion

The Octet Rule To draw the electron configuration of a neutral atom, look at the ATOMIC NUMBER. Neutral atoms have the same number of electrons and protons The first shell only holds 2 electrons Every other shell is filled up to 8 electrons The “left over” electrons are found on the last shell. The last shell is the valence shell and these electrons are called valence electrons. Valence electrons tell us which atoms will likely combine with others in order to ‘share’ 8 electrons on their last shell. All matter wants to be stable.

ATOMIC MASS The atomic mass tells us how heavy an atom is. The mass is calculated by the total protons and neutrons in the nucleus of an atom. Electrons are so tiny their mass is not counted in the overall mass of an atom. Their mass is considered negligible.