The Atom

What is an Atom? Atom: Smallest unit of all matter 3 Main Parts: 1) Proton (+ charge) 2) Neutron (No charge) 3) Electron (- charge) Protons & Electrons usually equal in number Elements (substance made of only 1 type of atom) are identified on the Periodic Table (page R36)

Reading the Periodic Table Atomic Number: Number of protons (+) the atom contains Usually # of electrons also Atomic Mass: Combined # of protons and neutrons inside the nucleus Electrons too small to affect mass How many protons, electrons, and neutrons does Carbon contain? Protons = ______ Electrons = ______ Neutrons = ______ 6 6 6

What’s the: Atomic number of Beryllium? B) Atomic mass of Beryllium? 4 C) How many protons? D) How many electrons? E) How many neutrons? 4 9 4 4 5

Electron Cloud Electrons orbit the nucleus in “energy levels” 1st level: closest to nucleus stable w/ 2 electrons 2nd level: stable w/ 8 electrons 3rd level: Atoms are stable when the outermost level is “full” Examine Carbon below. It has 2 electrons in the first level and 4 electrons in the 2nd level. Is Carbon stable?

Molecules Molecule: 2 or more atoms held together by a covalent bond Form when atoms are unstable Covalent Bond: Chemical bond where atoms share electrons Ex: Oxygen atom Why unstable? Only 6 electrons in outer energy level What happens? Each oxygen atom will share two electrons with the other oxygen End result? Both will have 8 electrons in its outer level (O2 is created) Molecules

Ionic Bonds Ionic bond: chemical bond where electrons are gained/lost sodium chlorine Ionic bond: chemical bond where electrons are gained/lost Creates Ions (atoms with + or – charge) Held together by magnetic attraction Cause: 1 atom steals an electron(s) from another atom Ex: Sodium + Chlorine = Sodium Chloride

Ionic Bonds 11+ 17+ 11+ 17+ 10- 18- 11- 17- +1 -1 Na Cl Na Cl e e e e sodium e e e e e e chlorine e e e e e e e e e After bonding Before bonding Na Cl Protons (+) Electrons (-) Net charge Na Cl Protons (+) Electrons (-) Net charge 11+ 17+ 11+ 17+ 10- 18- 11- 17- +1 -1

Quick Review Atoms become stable when their outer electron level is “full” Molecules created when 2 or more atoms combine together Covalent Molecules: share electrons Ions: lose and gain electrons