ch 5 atomic structure and the periodic table

1

5.1 Atoms are the smallest form of elements

1

2

All matter is made of atomsSame type of atoms = elementThere are approximately 100

elements known today

2

John Dalton is famous for studies involving atoms (early 1800s)

His work helped contributeTo the modern-day atomicTheory.

3

4

Each has its own symbol & propertiesHydrogen is the most abundant in

the universeOxygen is the most abundant in the

Earth’s crust

5

Each element is made of a different atom

Atoms are made of 3 different particles (subatomic particles)Protons, + chargeNeutrons, 0 chargeElectrons, - charge

5

6

Nucleus—center of the atom; contains the protons & neutrons

Electron cloud (or energy levels)—contains the electrons which orbit the

nucleusElectrons are 2000x smaller than the protons & neutrons

7

Energy LevelsCarbon has 2 energy levels

8

Atomic #--number of protons and total # of electrons in an atom

8

9

Atomic mass Mass of electrons is negligible (so small

it doesn’t really count)Avogrado’s # = 6.022 X 10 to the 23rd

power16 grams of oxygen would have Avogrado’s # of atoms in itThis also considered to be 1 mole

10

# Neutrons = Atomic mass – atomic #

11

Isotopes—atoms of the same element with different #s of neutrons

Atomic mass is the ave. # of all isotopesAn isotope is written with a numeral

after the name; the numeral represents the atomic mass

Examples Potassium Bohr Model

Potassium 40 = 21 neutrons40 is the atomic massatomic mass – atomic #40 – 19 = 21

Potassium 41 = 22 neutrons

Potassium 42 = 23 neutrons

12

13

Atoms form ionsIons form when atoms gain or lose

electronsElectrons have a negative charge

Gaining = negative ions (anions)Losing = positive ions (cations)

13

14

15

5.2 Elements make up the periodic tableElements can be organized by similaritiesMendeleev made the 1st periodic table

He ordered the elements according to atomic massesHe placed those with similar properties in the same row

15

16

The periodic table organizes the atoms of the elements by properties & atomic #

16

17

Group (or family)—Column of elements with similar properties

17

Families & IonsThe elements in the following families may form

these ions:

Family 1 = +1 Family 2 = +2Family 13 = +3

Family 17 = -1Family 16 = -2Family 15 = -3

18

19

Period—row of elementsThese elements have chemical

properties that tend to change the same way across the chart

Properties like atomic size, density, & likelihood to form ions vary in regular ways up, down, & across the chart

20

5.3 Periodic Table is a map of the elementsPeriodic table has distinct regions

Position on the table reveals something about the element (like how reactive it is)

Groups 1 & 17 are very reactiveGroup 18 is the least reactive (they are

stable)

20

21

Most elements are metalsMetals—usually shiny, conduct

electricity & heat well, can be easily shaped & drawn into a wire

21

Metals1. Reactive—families 1 & 2

Alkali metals (family 1)Alkaline earth metals (family 2)

2. Transition—more stable than the reactive metals

3. Rare earth –referred to as the “lathanides”4. Actinides--radioactive

22

23

Alkali metals & alkaline earth metals—at the left of the table & are very reactive

24

Transitions metals—near the center & include copper, gold, silver, iron

25

Rare earth metals—in the top row of the 2 rows of metals shown outside the main body of the table

Bottom 2 rows—separated from the table to save space

25

26

Common Properties of the Rare Earths These common properties apply to both the lanthanides

and actinides. The rare earths are silver, silvery-white, or gray metals. The metals have a high luster, but tarnish readily in air. The metals have high electrical conductivity. The rare earths share many common properties. This makes

them difficult to separate or even distinguish from each other.

There are very small differences in solubility and complex formation between the rare earths.

The rare earth metals naturally occur together in minerals (e.g., monazite is a mixed rare earth phosphate).

Rare earths are found with non-metals, usually in the 3+ oxidation state. There is little tendency to vary the valence. (Europium also has a valence of 2+ and cerium also a valence of 4+.)

27

Nonmetals1. Halogens—group 17, very reactive

nonmetals that can easily form salts2. Noble gases—group 18, very stable, can be

used to make light bulbs3. Metalloids—properties of both metals &

nonmetals, make good semiconductors found in electronics

28

29

Nonmetals & metalloids have a wide range of propertiesNonmetals are on the right side of

the tableC, N, O, SExtremely reactive halogens—Cl, I Noble (inert) gases like Ne (non-reactive)

29

30

Nonmetals/Halogens

31

Noble Gases (inert = non reactive = stable)

32

Metalloids lie between metals & nonmetals—they have characteristics of BOTH metals & nonmetalsMake good semiconductors in

electronic devices(computer chips)

33

Some atoms can change their identitiesRadioactive decay

Atomic nucleus is held together by forcesSometimes there can be too many or too few neutrons so these forces cannot hold it together properlyTo regain stability, the nucleus will produce particles & eject them

33

34

RadioactivityIdentity of radioactive atoms changes when the #

of protons changeHalf life—amount of time needed for ½ of the

atoms in a particular sample to decayCan be thousands or millions of yearsNEVER decays to zero!!

34

35

If half life is 25 years…