Structure of Atoms

What is an atom? Atom: the smallest unit of matter that retains the identity of the substance First proposed by Democratus (without any evidence) Everything ‘real,’ that takes up space and has mass, is made of tiny atoms.

What are the 5 parts of an atom? Atoms 2 regions: ◦ 1) Nucleus: the center of the atom that contains most of the mass of the atom ◦ 2) Electron shells: region that surrounds the nucleus that contains most of the space in the atom Nucleus Electron shells

What are the 5 parts of an atom? 3 subatomic particles ◦ 1) Protons: positively charged particles ◦ 2) Neutrons: neutrally charged particles ◦ 3) Electrons: negatively charged particles In nucleus In electron shells

Atomic Anatomy The guts of an atom “Subatomic Particles” Particle (symbol) MassCharg e Locati on Proton p + 1 amu+nucleus neutron n 0 1 amu0nucleus Electron e amu -Electron shells What they look like Nucleus # electrons = # protons (usually) e-

What does each atom look like? Every element has a square on the Periodic Table 8 O Oxygen Parts of the square Atomic #: # of protons And same # of electrons Symbol: 1 st letter always capital 2 nd letter lowercase Name Atomic Mass: # of protons + # neutrons # neutrons = mass – atomic # (Hint: round mass)

Atoms are electronically neutral  (have no overall charge) The # electrons = the # protons ◦ # e - = # p + = atomic # Overall charge of an atom

Practice finding # e -, p + and n 0 ElementProtonsElectronsNeutrons 7 N Nitrogen P Phosphorus Na Sodium = = = 12

More Practice ElementProtonsElectronsNeutrons 5 B Boron Ca Calcium He Helium = = = 2

Ex: Li- Three protons (atomic number.) P+P+ 3 Li Lithium So how do we draw the atoms? P+P+ P+P+

Four neutrons. (mass – atomic number.) 3 Li Lithium o o o o n0n0 n0n0 n0n0 n0n0 P+P+ P+P+ P+P+

Three electrons, In two electron shells. 3 Li Lithium o o o n0n0 n0n0 n0n0 n0n0 P+P+ P+P+ P+P+ e-

You start filling electron shells with the shell closest to the nucleus. How do I know what shells to put the electrons in? Shell ## of e- 12Go in as a pair 281 in each of 4 corners then pair up 38 (sort of-more to come) 1 in each of 4 corners then pair up 48 (sort of-more to come) 1 in each of 4 corners then pair up

What do I need to Know? You must be able to draw elements 1-36 Everyone should know the name/chemical symbol for elements 1-36 plus gold, sliver, mercury, and lead

To check your understanding, draw an atom of Sodium (Na). 11 Na Sodium

11 p + 12 n 0 11 Na Sodium For bigger atoms, it is easier to write the number of protons and neutrons in the nucleus, than draw each of them out. You should always draw each electron. e- Bohr Model of a sodium atom