smallest unit of an element that retains the properties of that element.

(+) positive charge Inside Nucleus 1 amu* Inside Nucleus no charge 1 amu* (-) negative charge no mass (≈ zero) Outside Nucleus *amu (atomic mass unit)

amu (atomic mass unit): the mass of something as small as a proton, (1 amu (atomic mass unit): the mass of something as small as a proton, (1.67 x 10-24 g), is not a very convenient number to work with. So, scientist came up with a relative atomic mass system that would make these measurements easier to use. It was arbitrarily decided that the carbon-12 atom would be the standard for comparison for all other atoms. The masses of all other atoms are expressed in comparison to the carbon-12 atom. One amu is equal to 1/12 the mass of the carbon-12 atom. Since carbon-12 has 6 protons and 6 neutrons, the amu for one proton or neutron is equal to 1 amu. amu (atomic mass unit) = 1/12 the mass of carbon-12 1 proton = 1 amu 1 neutron = 1 amu 1 electron = 0 amu

p+ +1 1 1.67 x 10-24 n0 1 1.67 x 10-24 e- -1 1/1840 9.11 x 10-28

The Nucleus Protons & Neutrons Electron Cloud Positively Charged Almost All of the Mass of the Atom Electron Cloud Where the Electrons are Found Almost All of the Volume of the Atom

Protons Neutrons Electrons Positive Charge No Charge Negative Charge Most of the atom’s Mass. Most of the atom’s Volume.

Quarks and Leptons: Quarks they are seen as the "elementary particles” of matter In the present standard model, there are six "flavors" (types) of quarks and leptons. Quarks make up protons & neutrons 6 “flavors” (types) 3 quarks = 1 proton or 1 neutron gluons: Neutrons: 2 downs & 1 up quarks Protons: 2 ups & 1 down quarks Electrons are Leptons QUARKS

Atoms are incredibly small. Atoms are measured in picometers (pm) — 1 pm = 10-12 m — Hydrogen, the smallest atom, measures only a 32 pm radius Nucleus- very small compared to the whole atom Density of the nucleus 1014 g/cm3 (2 x 108 metric tons/cm3!) If the atom was the size of an NFL stadium… the nucleus would be the size of a marble on the fifty yard line… …and the electron cloud would be the rest of the stadium for the electrons to run around in.

Atomic number is represented by Z Atomic Number = number of protons # of protons determines kind of atom (determines the element!) Atomic Number = number of electrons in a neutral atom! Mass Number = sum of protons + neutrons Atomic number is represented by Z Z = #p+

What’s the difference between these two carbon nuclei Atomic Number = number of protons # of protons determines kind of atom (determines the element!) Atomic Number = number of electrons in a neutral atom! Mass Number = sum of protons + neutrons Mass Number What’s the difference between these two carbon nuclei Atomic Number

(if it’s a neutral atom!) Mass Number # p+ + # n0 = mass # Atomic Number 12(mass #) - 6 (# p+)At.# 6 (# n0) Atomic # = # p+ & # e- (if it’s a neutral atom!)

Hyphen notation- the mass number is written with a hyphen after the element name- (spelled out- not symbol) copper-65 Nuclear symbol- the subscript = atomic # the superscript = mass #

Atomic #29 = 29 p+ & 29 e- Mass # = p+ + n0 So, Mass # - p+ = n0 65 – 29 p+ = 36 n0

= 3 = 7 + = 3 = 4 = 3

= 27 = 59 = 27 = 32 = 27

= 53 = 127 = 53 = 74 = 53

= 21 = 24 = 21

= 63 = 152 = 63 Europium-152

= 78 = 195 = 78 Platinum

Cu Copper 29 Atomic Number Element Name 63.546 Element Symbol Average Atomic Mass

Copper Cu 63.546 29

Mg 24.3050 24 12 12 12 12 Br 79.904 80 35 35 45 35 Cd 112.411 112 48 48 64 48 Mg 24.3050 12 Br 79.904 35 Cd 112.411 48

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