Topic 4 & 5Discovering Elements

&The Periodic Table

The periodic table is made of elements◦ What are elements?

Pure substances that cannot be broken down into simpler substances

Protons (+):◦ Positively charged◦ Same as the atomic number

Neutrons (neutral)

Electrons (-) ◦ Negatively charged

Each element is made up of:

1850’s: there were 58 known elements◦ Today there are 112!

◦ Scientists tried to organize elements

Atomic mass: the average mass of an atom of an element

The Periodic Table

Russian chemist He wrote down information about elements

on cards and put elements with similar properties in columns.

Dmitri Mendeleev

When Mendeleev arranged elements in order of increasing atomic mass, he found that some properties were similar!

He left some gaps in the table for elements that he thought would eventually be there based on properties.

Putting Elements in Order

By about 1915, the periodic table became based on a special number for each element, called its atomic number:◦ Is the number of protons an element has in its

nucleus.

Let’s

Label

this!

All atoms are neutral◦ Their positive and negative charges balance◦ SO, atoms contain an equal number of electrons

and protons

The total number of protons and neutrons in an atom.

# of protons + # of neutrons = mass number

How do we find the number of neutrons?

Mass Number:

Mass number – atomic number = # of neutrons

Let’s do some!!How many neutrons do the following elements

have? a. magnesium b. nitrogen

c. argon d. copper e. hydrogen

Each element has a symbol of 1-2 letters◦ Ex: Ag – silver, H - hydrogen

Elements are commonly named after the people who have discovered them◦ Ex: Einstein- Einsteinium

Element Symbols

Fill in the following table:

Element Name

Element Symbol

#of Protons # of Electrons

# of Neutrons

carbon

O

16

aluminum

34

lithium

Ne

79

barium

Page 117◦ Symbols for Elements

# 1-5 (procedure)

To Do:

http://www.youtube.com/watch?v=GFIvXVMbII0

The Periodic Table

GROUPS/FAMILIES: (1-18)◦ VERTICAL◦ UP and DOWN◦ Usually have common properties

PERIODS: (1-7)◦ Horizontal◦ LEFT TO RIGHT

How is it organized?Groups and Periods

LABEL

The “STAIRCASE”

LABEL

Separates metals from non-metals.

The elements touching the staircase: These are called METALLOIDS.

◦ Have properties of both metals and non-metals◦ Few in number◦ Solids

The “Staircase”

LABEL

Good conductors of heat and electricity

Bright metallic shine (lustre)

Easily shaped (malleable)

Solids (except mercury)

Poor conductors of heat and electricity

Dull, various colours

Brittle Solid or gas

(except bromine)

METALS vs. NON-METALS

Metals in the periodic table that run from Group 3 to the staircase.

Metal properties

Transition Metals

Metals are to the left of the staircase

Non-metals are to the right of the staircase

LABEL

Except for hydrogen Most reactive

◦ Require special storage Why?

◦ Each alkali metal has an unpaired electron and tends to get rid of the electron by forming a compound

List them!

http://www.youtube.com/watch?v=m55kgyApYrY

Group 1- Alkali Metals

LABEL

Similar to group 1, but they are not as intense

Ex: magnesium reacts with water but less vigorously than sodium does.

List them!

Group 2- Alkaline Earth Metals

LABEL

Very un-reactive – INERT Is a useful property when it comes to light

bulbs!◦ Argon is commonly used inside a light bulb to

keep the tungsten from burning out Stable

◦ Do not have any unpaired electrons List them!

Group 18- Noble Gases

LABEL

Naturally found in compounds because they react vigorously with almost every other element

Also have an unpaired electron◦ They GAIN an electron◦ Corrosive and harmful

List them

Group 17- Halogens

LABEL