ATOMS & THE PERIODIC

TABLE

Subatomic Particles

• Protons and electrons are the only particles that have a charge.

• Protons and neutrons have essentially the same mass.

• The mass of an electron is so small we ignore it.

Atoms and the Periodic Table

Subatomic Particle

Location Charge Size Mass

Protonp+

Nucleus Positive1+

About same as neutronD = 10-15 m

1 amu1.6726 x 10-24 g

Neutronn0

Nucleus No chargeNeutral

0

About same as protonD = 10-15 m

1 amu1.6749 x 10-24 g

Electrone-

Orbital cloud

Negative1-

Tiny compared to

proton & neutron

D = 10-18 m

1/1840 amu9.11 x 10-28 g

Size of Atoms

Particle Diameter (meters)atom 10-10

nucleus 10-14

proton 10-15

neutron 10-15

electron 10-18

1 Angstrom = 10-10 m

History of the Atomic ModelDemocritus – 400 BC

atoms make up all substances

John Dalton – 1766-1844atom is a solid hard sphere

Joseph John Thomson – 1856-1940discovered the electron in 1897plum pudding model of atompositive sphere with negative e- embedded

• Lived from (1766-1844)• All elements are composed of atoms• Atoms of the same element are identical.

Each element has unique properties .• Atoms of different elements can be

chemically combined in simple whole number ratios to form compounds.

• Law of Conservation of Matter/Mass

The Electron

• Streams of negatively charged particles were found from cathode tubes.

• J. J. Thompson is credited with their discovery (1897).

The Atom, circa 1900:

• “Plum pudding” model, put forward by Thompson.

• Positive sphere of matter with negative electrons imbedded in it.

Ernest Rutherford – 1871-1937gold foil experimentmost of atom empty spacepositive nucleus contains most of the massdiscovered protons in 1919

James Chadwick – 1891-1974discovered the neutron in 1932.

Niels Bohr – 1885-1962 (Danish)electrons move around the nucleus in fixed

orbits that have a set amount of energy

Electron Cloud Model of Atom1. came to be used to estimate the positions of electrons in an atom2. uncertainty principle, which states that it is not possible to obtain precise values of both position and momentum of a particle at the

same time3. probability of finding an electron

Protons• The number of protons distinguished 1 atom

from another• Most atoms are very stable• It takes a lot of energy to add or remove a

proton from an atom• Atomic number = number of protons• The Periodic Table is arranged by number of

protons

Symbols of Elements

Elements are symbolized by one or two letters.

Atomic Number

Number of protons = The atomic number

Atomic Mass

The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

Mass Number

• The number of protons plus neutrons in an atom.

• Always a whole number.• Written or indicated like this:

H C Cu Si K

Calculating Number of Neutrons

• Subtract:

Mass Number - Atomic Number = Neutrons

Mass Number - # of protons = Neutrons

Notes on Finding Numbers of Protons, Neutrons, Electrons

Isotopes• Atoms of the same element with different

numbers of neutrons

Isotopes

• To distinguish between isotopes of an element

• Ex: Neon has 3 main isotopes

Neon Protons Neutrons Mass number

Ne-20 10 10 20Ne-21 10 11 21Ne-22 10 12 22

Average Atomic Mass

• Atomic mass unit – 1/12 the mass of a C-12 atom

• To calculate avg. atomic mass

Cesium Natural % Abundance

Mass Number

Avg. Atomic Mass

Cs-133 75% 133 99.75

Cs-132 20% 132 26.4

Cs-134 5% 134 6.7

Example – Avg. Atomic Mass

Chemical Goals

• To be Chemically StableUnstable atoms are radioactive: their nuclei change or decay by spitting out radiation, in the form of particles or electromagnetic waves.

• To be Electronically neutralTo have no charge on the atom. To have the same # of protons as electrons.

Why does an atom stay together?

The strong nuclear force keeps protons and neutrons together in the nucleus in spite of the repulsion of the protons for each other.

The strong nuclear force acts only over a very short distance. It doesn’t work outside the nucleus.

The strong nuclear force is stronger than the electromagnetic force.

Valence Electrons• Electrons in outer energy level.• Can only have 8 or less. This is the Octet Rule.• These electrons are the ones involved in

bonding with other atoms and the ones with the most energy.

• Looking at the Periodic Table, you can tell the number of valence electrons for the A Families from the Roman Numeral designation

Electrons

1. e- located far from nucleus in a series of energy levels.

2. Each e- has a certain amount of energy.

3. The further the e- gets from the nucleus the more energy it has. Valence e- have the most energy. Those closest to the nucleus have the least amount of energy.

Energy Levels

1. Each energy level can only hold a certain number of e-

2. Electrons always fill low energy orbitals (closest to

the nucleus) before filling higher energy ones.

3. The high the energy level occupied by the e-, the easier it is for the e- to escape from the atom.

4. Quantum of energy – amount of energy needed to move an e- from its present energy level to the next one

5. Ground State – the lowest energy level for

an e-.

Electron Placement on the Periodic Table

2 e-

8 e-

18 e-

32 e-

Type of Sublevel

Number of orbitals in Sublevel

Number of electrons in

orbital

s 1 2

p 3 6

d 5 10

f 7 14

Principal Energy Level

(n)

Number of Sublevels

Type of Sublevel(Atomic Orbitals)

Number of Electrons

2n2

1 1 s 2

2 2 s, p s-2, p-6 = 8

3 3 s, p, d s-2, p-6,d-10 = 18

4 4 s, p, d, f s-2, p-6,d-10, f-14

= 32

Electron Configuration Chart

Aufbau /Orbital Diagram

EX: Electron Configuration for Potassium 19 electrons

EX: Electron Configuration for Arsenic 33 electrons

EX: Electron Configuration for Silver 47 electrons

Pauli Exclusion Principle

• An orbital can hold 0, 1, or 2 electrons and if there are 2 electrons in the orbital they must have opposite spin.

Aufbau Principle

• Rules for Orbital Filling• Lower-energy orbitals fill first.• An orbital can hold only 2 e- with opposite

spins.• The most stable arrangement for e- is one

with the maximum number of unpaired e-. This minimized e- to e- repulsion and stabilizes the atom. – Hund’s Rule

Hund’s Rule

• When filling up sublevels other than s, electrons are placed in individual orbitals before they are paired up.

Increasing Energy in Electron Sublevels

THE DIAGONAL RULE MUST GO IN THIS ORDER: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d and 7p. These orbitals will account for all the elements now known. This diagonal rule can help account for the octet rule, too.

The Energy Flow

• The order of increasing energy of the orbitals is then read off by following these arrows, starting at the top of the first line and then proceeding on to the second, third, fourth lines, and so on. This diagram predicts the following order of increasing energy for atomic orbitals.

• 1s < 2s < 2p < 3s < 3p <4s < 3d <4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p < 8s ...

Bohr Model of Atomsonly represents energy levels, not orbitals

Lithium

Nobel GasesNeon

Argon

Krypton

Drawing AtomsThe Bohr Model

e- 3 p+

11 p+

Lewis StructuresElectron Dot Diagrams

• Describes e- arrangement in atoms • Describes bond arrangement in molecules.• Uses dots to represent valence e- around an

atom• EX:

Li Ne O Si

Dimitri Mendeleev• In the late 1860's, Mendeleev

began working on his great achievement: the periodic table of the elements. By arranging all of the 63 elements then known by their atomic weights, he managed to organize them into groups possessing similar properties. Where a gap existed in the table, he predicted a new element would one day be found and deduced its properties. And he was right. Three of those elements were found during his lifetime: gallium, scandium, and germanium.

Mendeleev’s Periodic Table

Moseley’s Periodic Table

In 1913 Henry Moseley came up with this Periodic Table. The elements are arranged by increasing atomic number.

• A group (also known as a family) is a vertical column in the periodic table of the chemical elements. There are 18 groups in the standard periodic table.

• Elements in a group have similar configurations of the outermost electron of their atoms – same number of valence e-

• This gives the groups of elements similar physical and chemical characteristics.

• With each group across a period, the elements have one more proton and electron and become less metallic.

• Rows of elements are called periods. The period number of an element signifies the highest unexcited energy level for an electron in that element.

Physical Properties

Metals• Good electrical conductors

and heat conductors. • Malleable - can be beaten

into thin sheets. • Ductile - can be stretched

into wire. • Possess metallic luster. • Opaque as thin sheet. • Solid at room temperature

(except Hg).

Nonmetals• Poor conductors of heat

and electricity. • Brittle - if a solid. • Nonductile. • Do not possess metallic

luster. • Transparent as a thin sheet. • Solids, liquids or gases at

room temperature.

Chemical Properties

Metals• Usually have 1-3 electrons

in their outer shell. • Lose their valence electrons

easily. • Have lower

electronegativities.

Nonmetals• Usually have 4-8 electrons

in their outer shell. • Gain or share valence

electrons easily. • Have higher

electronegativities.

Metalloids

• Electronegativities and ionization energies between those of metals and nonmetals

• Possess some characteristics of metals/some of nonmetals

• Reactivity depends on properties of other elements in reaction

• Often make good semiconductors• Boron, Silicon, Germanium, Arsenic, Antimony,

Tellurium, Polonium

Ionic BondingBetween Metals & Nonmetals

Metals• Make Ionic Compounds• Lose Electrons• Have positive oxidation

numbers• Are first in a formula

Ex: Na2S

• When naming, write the name just as it is

• Ex: Sodium sulfide

Nonmetals• Make Ionic Compounds• Gain Electrons• Have negative oxidation

number• Are second in the formula

Ex: MgO• When naming, drop the

ending of the name and add IDE

• Ex: Magnesium oxide

More Ionic Bonding

• Strong attractions or forces between atoms in these compounds

• High melting and boiling points, good conductors

• Have a lattice structure

Sodium chloride Lattice

Covalent BondingCovalent Molecules

• Between 2 or more nonmetals• Share electrons• Still try to obey the Octet Rule• Weak bonds between molecules but strong

bonds between atoms• Low melting and boiling points, usually non

conductors• Simple molecules or giant structures can form

More Covalent Bonding

• Diamond and graphite are held together by this type of bond (allotropes)

• Ex: H2O, H2O2, CH4, CO2

• Ex: Diatomics – H2, N2, O2, F2, Cl2, Br2, I2

Water Molecule

Moles•The mole is the SI unit for amount of substance

•A mole (abbreviated mol) is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.

Avogadro’s Number

• 6.02 x 1023 – is the number of particles in exactly one mole of a pure substance.

• Conversion factor!• 6.02 x 1023 particles = 1 mole

If I have 3.45 moles of hydrogen, how many particles do I have?

6.02 x 1023 = 1 Mole