The History Of Matter

Section 1Grade 9 Science

Objectives

• Review the development of scientific thought as it relates to matter and the atomic structure.

• Define element and understand its relationship to the concept of matter.

• Describe the understanding of the structure of the atom.

Democritus (460-370 BC)• Hypothezised matter was

tiny particles in constant motion.

• Cannot be broken apart – solid.

• Eternal (unable to create or destroy)

• Surrounded by an empty space.

*called particles atomos – meaning “indivisible” - ATOM

Aristotle (384 BC – 322 BC)• Ancient Greek philosopher.• Believed matter was made of four elements.• His theory was accepted by all.

Alchemy and the Middle Ages • Concerned with metallurgy (study of properties of metals).

• Goals - turn common metals into gold or silver.– - find a substance to give eternal life.

–(the key to both is called the Philosopher’s Stone)

•Developed observation, experimentation, measurement and classification – first “scientists.”

• Called “alchemists”

Lavoisier (1743-1794)• Father of modern

Chemistry• Defined the term

ELEMENT - a fundamental pure substance that cannot be broken down into simpler parts.

• Discovered many elements including water and hydrogen. (23 elements)

Dalton (1766-1844)• FIRST ATOMIC THEORY • all matter is made of indivisible

particles - atoms.

• Atoms of each element are unique (differ by mass).

• Compounds are combinations of different elemental atoms.

• Atoms cannot be created or destroyed.• (Law of conservation of

matter)

Thomson (1773-1852)• Hypothesized that the first

subatomic particles were electrons.

Electrons have a small mass and

negative electric charge.

• Atom is sphere with equal number of positive charges mixed with negative electrons - Plum pudding model.

• Overall atom has a neutral charge.

Rutherford (1871-1937)• Conducted “Gold Foil Experiment.”

• Discovered the atomic nucleus.

• Nucleus is a small, dense (heavy), positively charged core.

• Positive charges due to another subatomic particle called protons

• Hypothesized atom composed of mostly space with a centre

• nucleus and small electrons floating around.

http://www.glencoe.com/sec/science/cgi-bin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link=http://micro.magnet.fsu.edu/electromag/java/rutherford/

Chadwick (1891-1974)• discovered the neutron in

the nucleus

• Neutrons have no charge and are the size of protons.

• THREE subatomic particles:• - dense positive

nucleus (protons and neutrons).

• - negative electrons floated around.

Thompson-

Rutherford-

Chadwick-

The Atom & Element

Section 2Grade 9 Science

Objectives

• Define element and identify symbols of some of the common elements.

• Explain and draw a Bohr model of an atom.

• Understand the movement of electrons when energized.

• Understand and perform a Flame Test

• Compare and contrast positive and negative ions.

Everything you wanted to know about

The Atom• Contains 3 subatomic particles:

• The dense center (nucleus) of the atom contains:

Neutron - a particle with no charge. Proton - a particle with a positive

charge.

• Electrons are tiny particles that move around the nucleus.

- negative electrical charge. - same # of positive and negative charges = neutral.

Definitions

• element - a basic substance that can't be simplified (hydrogen, oxygen, aluminum)

• atom - the smallest amount of an element• molecule - two or more atoms that are

chemically joined together (H2, O2, H2O, etc...)• compound - a molecule that contains more

than one element (H2O, C6H12O6, etc...)

Elements, Elements, Elements!• Chemical Symbol: abbreviation of the name of

the element, usually based on a Latin name. – Eg. Gold (Au) from latin name Aurum– Eg. Silver (Ag) from latin name Argentum– Eg. Lead (Pb) from latin name Plumbum

Elements to learn… and memorize!H, He, Li, Be, B, C, N, O, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Fe, Ni, Cu, Zn, I, Ag, Sn, Au, W, Hg, Pb, U

CREATE A PERIODIC TABLE

Atomic Mass = # of protons + # of neutrons

# of neutrons = Atomic mass – Atomic #

The Bohr Model• hypothesized electrons occupy

precise positions.

• specific distances around the nucleus called orbits or shells.

• only a specific number of electrons can occupy each orbit.

• called the “planetary model”

Electrons occupy the closest orbital first.

• 1st – holds 2 electrons (e-)

• 2nd – holds 8 e-

• 3rd – holds 8 e-

Ever element has a different number of electrons.

Al= Aluminum (13 electrons)

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Periodic Families and

Groups

Section 2Grade 9 Science

Alkali Metals (IA)

• All shiny, soft, silvery, highly reactive metals because they all have 1 electron in their outer shell which they loose easily.

• All react with water

• Hydrogen is in this family column because it has 1 valence electron.

Hydrogen is in a family by itself because of special properties. (gas not a solid)

Alkaline Earth Metals (IIA)

Be

Mg

Ca

Sr

Ba

Ra

Beryllium

Magnesium

Calcium

Strontium

Barium

Radium

Common Characteristic…• Shiny, silvery and white• React with water• 2 valance electrons• Low electron affinities- Do not gain

electrons easily to make positively charged ions.

Halogens (VII-A)

Fluorine

Chlorine

Bromine

Iodine

Astatine

Common Characteristics…• All non-metals• The only group that has

elements at all 3 states (solid, liquid, gas)

• All have 7 valence electrons.

Noble Gases (VIII-A)

HeNeArKrXeRn Radon

Common Characteristic…

• All odorless, colorless, with very low chemical reactivity.

• All have full outer shells which is why they are almost non-reactive.

Daily use includes lights, welding, scuba diving,

signs.

Metals, Non-Metals and Metalloids

Metals (green)• Shiny 'metallic' appearance • Solids at room temperature (except mercury)

• High melting points • High densities • Low ionization energies • Low electronegativity • Thermal conductors (attract heat)

• Electrical conductors (eg. Metal pole in a lighting storm)

• Most Metals will lose e-

Colour Element

green copper

yellow sodium

red strontium

yellow-green barium

orange-red calcium

purple potassium

purple-red lithium

Elements give off a unique colour of light when heated - used to detect the presence of a metal

This is known as a flame test.

Bohr model explains the colours as “jumps” electrons make when energy is added.

Flame Test• Energy (heat, light, electrical) causes electrons

to ‘jump’ from orbit to orbit. • When electrons drop back down to previous

orbit they release the energy as light.

• Elements have different number of electrons

– different “jumps” – different spectrum of color.

Non-Metals (orange)• poor conductors of heat and

electricity• they form acidic oxides (whereas metals generally form basic oxides)

• dull and brittle• lower densities• lower melting points and boiling

points • high electronegativity• nonmetals will gain e-.

Metalloids (Purple)• Have characteristic

between both metals and non metals.

• commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.

• metallic-looking brittle solids

Bonding & Compounds

Section 2Grade 9 Science

Reactivity• An elements reactivity it dependent on the

number of electrons in the outer shell. • Elements want to have full orbits; the easier it

is to achieve that, the more reactive they are.The fewer the electrons in the outer shell, the more reactive and vice

versa.

• Chemical reactions occur as atoms work together to try to obtain a full outer orbit of valence electrons.

• An atom with a FULL outer orbit is very stable

• Atoms will acquire a full outer shell in 3 ways:– Give away an e- to another atom.

- Take an e- from another atom.• When a neutral atom gives an e- away it ends

up with a positive charge.• The atom is now called a positive ION OR

Cation.

Sodium atom:11 p+

11 e-

Na

Sodium ion:

11 p+

10 e-

Na +

+

• Atoms that take an e- end up with a negative charge – called a negative ION (anion)

-

Chlorine atom:17 p+

17 e-

Cl

Chlorine ion:17 p+

18 e-

Cl -

Calcium atom:20 p+

20 e-

Ca

Calcium ion:20 p+

18 e-

Ca +2

Organization of the Periodic Table Lab

Compounds, can’t live without them!

• A compound forms when two or more elements join by forming bonds.

• Bonds form when electrons jump from the outer orbit of one element to the outer orbit of another. – Eg. NaCL

• Salt!

A Chemical Reaction:

• A movement of electrons between combining atoms that results in the formation of a NEW

substance.

• Produces heat.

• Pure substance• The particles that make up a substance are all the same kind.

• Mixture • Substance contains more than one kind of particle.

• Elements• The simplest form of a material; an atom is the smallest particle of

an element.

• Compounds• The simplest form of any material containing two or more

elements chemically bonded together.

• Molecule• the smallest particle of a compound.

• Element:• Silver– all atoms are pure silver.

• Compound:• Salt – all molecules are pure sodium chloride.

Possible to have a molecule of the same atoms:

Oxygen gas – O2 Hydrogen gas – H2

Molecules like this are diatomic – “two atoms.”

• Heterogeneous mixture· Particles are not evenly distributed.· Individual particles can be found.

• Homogeneous mixture· Particles of are evenly distributed – “solution”· Cannot easily separate different parts.

In summery…• The Atom

• - Atoms react or not depending on its electron structure.

• - All atoms desires to have a full outer electron shell.

• - Metals will lose e- and nonmetals will gain e-.

• - Ions combine to form compounds.

• - Like charges repel, opposite charges attract.

• - When elements combine in a chemical reaction to form a new compound ~ all have filled outer electron shells.

Chemical Formulas

Section 2Grade 9 Science

Chemical Formulas

H2 + Cl2 2 HCl

• Eg.

• The Law of Conservation of Matter:

• In any chemical reaction matter cannot be created or destroyed.

• Atoms will rearrange to form new compounds, but the number and type of atoms will not change

during the reaction.

subscript

Chemical formula - shows the type and amount of each atom present in a compound.

HOH

HH

O+

HH

OH

H

O

HH

O

H2O3

6 Atoms (3x2) of hydrogen and 3 atoms of oxygen combine to make 3 molecules of

water.

Compound Number of particles Total of each element

1KHCO3 1

3AlCl3 3

6CBr4 6

5H2SO4 5

4C11H22O12 4

Chemical vs. Physical Changes

Section 2Grade 9 Science

• The substance will remain the same even though it may change state or form.

• Changes may include colour, texture, odour, lustre, clarity, taste, state of matter, harness, malleability, melting point (mp), boiling point (bp) density, viscosity, and solubility.

Physical Change

Chemical Change• During a chemical change the original substance is

changed into one of more different substances that have different properties.

• Atoms stay the same but molecules are transformed so the products are different.

Identifying a Chemical Change

• 2 or more tests might be required to determine if a chemical change has occurred.

• C + O2 CO2 (Carbon mixes with oxygen to produce a new substance.)

• H2O(l) H2O(g) (liquid water changes into water vapour)

Physical or Chemical?• Margarine spoils in the fridge.• Chocolate melts in the sun.• A clear liquid is mixed with a base

and turns purple.• Leaves change from green to red,• Metal on a bike turns from silver to

reddish-brown.• Water disappears in a glass over

time.• Sawdust forms from wood being

cut with a saw.• CO2 is dissolved into carbonated

drinks.

Chemical Changes Around Us

• Work with a partner.• Write a list of as many chemical changes that

occur in our everyday lives, either man-made or natural.

• Eg. Corrosion• Eg. Digestion• Eg. Fertilizers