#### Transcript Chapter Two Atoms & The Periodic Table

```


Discuss logistics of homework
Quiz over Chapter 1
Chapter two notes
 Section 2.1
 Section 2.2
▪ Break
 Section 2.3
 Section 2.4
▪ Break
 Section 2.5
 Section 2.6

Atoms are the
smallest
quantities of
matter that still
retain the
property of that
matter


Democritus was the first to develop this idea
of an atom in the 5th century
John Dalton was the first to formalize the
idea of an atom with Dalton’s atomic theory
 Known as the “father of atomic theory”

The word “atom” comes from the Greek word
“atomos” meaning “uncuttable.”





All matter is made up of atoms
Atoms are indivisible
Atoms of the same element are identical
Atoms of one element are different than
atoms of another element
Atoms come together to form compounds

If two elements can combine to create
multiple compounds, then the ratios of the
masses of the second element which
combine with a fixed mass of the first
element will be ratios of small whole numbers

CO
100 g of C
133 g of O


CO2
100 g of C
266 g of O

Late 1800s; discovered by J.J. Thomson



Thomson performed many experiments with
variable electric fields and measured degree
of reflection
Charge-to-mass ratio
1.76 x 108 C/g (C stands for coulomb)


Early 1900s;
discovered by
Robert
Millikan
Oil Drop
Experiment

Millikan used Thomson’s charge-to-mass
ratio to determine the mass of an electron


Atoms are neutral; need for a positive particle
Thomson believed in the plum pudding
model

Rutherford contested this with the Gold Foil
Experiment

Rutherford proposed all of the atom’s
positive charge in the core of atom called the
nucleus

Protons: in the nucleus
 Provide same charge as electrons, only opposite
sign
 Provide the mass of the atom (nearly 2000 times
more massive than electrons)

Electrons: outside the nucleus
 Provide the volume of atom



Discovered by James Chadwick in 1932
Practically same mass as proton
No charge

Be back in 5!

Not all atoms of a given element are identical
 Most elements have 2 or more isotopes (atoms
with same # of protons, different # of neutrons)


Isotopes behave like each other
Named after their mass number
 Ex: U-235 (“Uranium two thirty five”)

Atoms with charges (different # of electrons)
 Positive ions called cations
 Negative ions called anions

List the number of protons, neutrons, and
electrons in the following elements:
Carbon-14

Iodine-128
An atom has a mass number of 114 and 66
neutrons. Write the isotope notation for this atom.

Mass of an atom in atomic mass units (a.m.u)
 Based off of 1/12 of a carbon atom

Most elements are mix of isotopes in nature
 Average Atomic Mass is reported

The atomic masses of two stable isotopes of
copper, copper-63 and copper 65, are
62.929599 and 64.927793 amu, respectively.
If copper-63 is 69.17% and copper-65 is
30.83%, what is the average atomic mass of
copper?

Be back in 5!

Mostly metals (left of stair step)
 Good conductors of heat/electricity

Non metals (right of stair step)
 Poor conductors of heat/electricity

Metalloids/Semi-metals (on stair step)
 Properties of both metal and nonmetal
 B, Si, Ge, As, Sb, Te, Po, At

Groups: vertical columns
 Elements in the same group share similar
chemical properties
 18 groups

Periods: horizontal rows
 Elements transition from metal to nonmetal
across a period

A unit of quantity (how much)
 Mole = mol

1 mole = 6.022 x 1023 “particles”
 “particles” can be atoms, molecules, or formula
units

Molar Mass = the mass of ONE MOLE of a
substance
 g/mol

1 mole of water = 18.02 grams

1 mole sodium chloride = 58.44 g

1 mole helium gas = 4.003 g

Molar mass is found by
 Listing elements in compound
 Determining their mass found on periodic table
 Multiplying by how many atoms there are
 Adding these values
 Ex: H2SO4

How many molecules of magnesium chloride
(MgCl2) are there in 67.35 grams of
magnesium chloride?

How many chlorine atoms are there in the
same mass of magnesium chloride?
1)Describe the contributions of Thomson, Millikan,
Rutherford, & Chadwick (include experiments where
applicable)
2)Write the appropriate symbol for the following: Z=28,
+3
A=64
3)How many protons, neutrons, & electrons in
4)Rb-85(72.17%) is 84.911794. If the average atomic
mass of Rb is 85.4678, what is the atomic mass of Rb87(27.83%).
5)Name 2 elements from each of the groups of the
periodic table discussed today
6)How many grams is 5.30 x 1023 molecules of K2O?
```