Chemistry & Matter 9

What is the history of atomic theory?

1. Democritus - 430 BC

2. Dalton - 1808

3. Thompson - 1897

4. Rutherford - 1911

5. Bohr - 1913

6. Chadwick - 1932

What did Democritus discover?

Matter is formed of small pieces that could not be cut into smaller parts called "atomos" meaning uncuttable

What did Dalton discover?

1. Atoms are tiny, invisible particles

2. Atoms of one element are all the same.

3. Atoms of different elements are alI different. 

4. Compounds form by combining atoms. 

What did Thompson discover?

Atoms are made mostly out of (+) charged materials (like dough in a bun). The (-) charged electrons are found inside the (+) dough

What did Rutherford discover?

Atoms have (+) particles in the center and are mostly empty space

• (+) particles are called protons

• The center of atoms is called the nucleus

What did Bohr discover?

Improved on Rutherford’s model- proposed that electrons move around the nucleus in specific layers/shells

What did Chadwick discover?

Worked with Rutherford to discover particles with no charger- called neutrons

• neutrons also found in nucleus

What do electrons do?

orbit around the nucleus

Describe subatomic particles

Protons - positively charged particles found in the nucleus

Neutrons - neutral particles found in the nucleus

Electrons - negatively charged particles that orbit the nucleus

Which scientist discovered how to arrange elements properly?

Russian scientist, Dmitri Mendeleev

• found out you could arrange elements based on chemical properties and atomic mass

What are Ions?

Ions are groups of atoms that carry a positive or negative charge

What is each row in the periodic table called?

Period

What is each column in the periodic table called?

Group

• have similar chemical properties

What are the 3 main groups of elements the periodic table can be broke into?

Non-metals. Metals, and Metalloids

What are Metals?

• lustrous (shiny)

• malleable (can be hammered into sheets)

• ductile (can be drawn into wires)

• solids at room temperature

• great conductors of electricity

What are non-metals?

• can be in any state

• not shiny

• brittle (fragile)

• poor conductors of electricity

What are metalloids?

have characteristics of both metal and non-metals

• can conduct electricity but not always very well

What are alkali metals?

most reactive metals

• have one electron in the outermost shell

• require extra storage

What are alkaline earth metals (Group 2)?

react when exposed to air and water

What are halogens (Group 17)?

Most reactive non-metals

• Naturally found in compounds

• have an unpaired electron but instead of giving it

  away, they gain another to form compounds

What are noble gases (Group 18)?

Chemically stable because they do not have any unpaired electrons (not reactive)

• Highly unlikely to take part in a chemical change

What is an ionic compound?

A compound formed when a metal transfers electrons to a non-metal

• creating oppositely charged ions that attract

What is a molecular compound?

a compound formed when two or more non-metals share electrons

• creating covalent bonds

What is an ion?

An atom that has gained or lost electrons

• giving atom a positive or negative charge

What is a valence electron?

An electron in the outermost shell of an atom

• these electrons are involved in bonding

What is a cation?

A positively charged ion formed when a metal loses electrons

How does a metal become a cation?

It loses valence electrons

• charge becomes positive

What is an anion?

A negatively charged ion formed when a non-metal gains electrons

How does a non-metal become an anion?

it gains electrons

• charge becomes negative

What is the transfer of electrons in covalent bonds?

there is NO transfer of electrons in covalent bonds

• non-metals SHARE electrons

What is the transfer of electrons in ionic bonding?

a metal gives electrons to a nonmetal

• forming ions that attract

What is a full valence shell?

When the outer electron shell has its maximum number 

• making the atom stable

Why does gaining an electron make an atom negative?

electrons are negative, so adding one gives more negatives (electrons) than positives (protons)

• atom becomes an anion

Why does losing an electron make an atom positive?

Losing a negative electron leaves more positive protons

• atom becomes cation

Why do electron move between atoms?

Atoms want to become want to become stable by filling or emptying their outer shell

• (octet rule)

What is the octet rule?

Atoms are most stable when they have 8 electrons in their outer (valence) shell

What are multivalent elements?

Metals that can form more than one possible ion charge

• they can lose different numbers of electrons

What are polyatomic ions?

A group of atoms bonded together that have an overall charge

Are ionic compounds conductive? Why?

yes, when melted or dissolved, because ions are free to move (Ions have charges) allowing electricity to flow

What is covalent and ionic bond?

Covalent - bond when non-metals share electrons

• forms molecules

Ionic - bond when metal transfers electrons to non-metal

• opposite charges attract

What are diatomic molecules?

Elements that naturally exist as two atoms bonded together

Why do elements have specific charges?

They gain or lose electrons in the easiest way to get a full valence shell and become stable

What are common charges by group?

Group 1 (alkali): +1

Group 2 (alkai earth): +2

Group 17 (halogens): -1

Group 16 (chalcogens): -2

What are catalysts?

is a substance that speed up the rate or reaction

• is present with reactants of a reaction, they are not consumed during a reaction

What is an enzyme?

Called a catalase

• a protein that speed up reaction

• found in many diff. types of animal and plant cells

• the shape of an enzyme molecule helps break the reactant down

Types of changing rates of reaction

Temperature

• reactant moves faster

Stirring

• keeps reactant particles in motion

Crushing

• greater surface area, more room available for reaction

Higher concentration (more solute)

• more atoms of each reactant available to react

What are inhibitors?

chemical/substances or conditions that slow down chemical reactions

• ex. hot or cold

What are 3 reactions involving oxygen?

• Combustion

• Corrosion

• Cellular Respiration

What is combustion?

when oxygen reacts with a substance to form a new substance and give off energy (heat)

What is corrosion?

slow chemical change when oxygen reacts with a metal

• ex. rusting

What is cellular respiration?

chemical reaction that takes place in the cells of your body

• food (glucose) reacts with oxygen to produce energy

What are endothermic reactions?

chemical reactions that absorb energy/heat

• corrosion

What are exothermic reactions?

chemical reactions that give off energy/heat

• cellular respiration

• combustion (fire)IB

How to prevent corrosion?

• painting

• galvanization

• cathodic protection

What happens when chemical bonds are broken?

energy is added

• endothermic

What happens when chemical bonds form?

energy is released

• exothermic

What is Galvanization?

coating metal with a layer of zinc to protect it from corrosion (rusting)

• zinc acts like a barrier and sacrifices itself for the corrosion

What is cathodic protection?

when a more reactive metal (like zinc) is attached to a metal so it will rust first

• mostly underwater and underground

5 Factors affecting reaction rate?

Stirring

Temperature

Catalysts

Surface Area

Concentration

What are chemical properties?

• reaction with acids

• reaction with water

• reaction to heat

• ability to burn

• behaviour in air

What are physical properties?

• colour

• lustre

• boiling point

• melting point

• mallaebility

• ductility

• crystal shape

• hardness

• conductivity

• density

What are Isotopes?

Atoms that are of the same element with the same number of protons but different number of neutrons

What two reactants are needed for corrosion?

Oxygen and water

Why do elements in the same group have similar chemical characteristics?

They have the same number of valence electrons

What are chemical changes ?

When a new substance forms

What are physical changes?

When a substance changes state

If temperature increases, what type of reaction is it?

Exothermic (heat is released)

If temperature decreases, what type of reaction is it?

Endothermic (heat is absorbed)

What does “most readily” mean?

Happens the fastest or easiest

How to know if compound conduct electricity?

• must have ions

• ions must be free to move (molten or dissolved in water)

• solid ions don’t conduct

What is oxidation?

A chemical reaction where a substance loses electrons

What are indicators?

Substances that change colour to show a chemical property of a solution

What is a solution?

Particles fully dissolved, clear

How to tell if a substance is a good insulator?

Low melting/Boiling point

How to tell if substance is a good conductor?

High melting/boiling point

What is electronegativity?

the ability of an atom to attract shared electrons