Valence Electrons Bohr Diagrams Atomic Structure Atoms have

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 • 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 1 Number of Electrons 2 2 8 3 8 4 18 5 18 6 32 7 32

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.