chemistry
What is Chemistry?
Chemistry is the science that studies MATTER,
What is MATTER?
• MATTER is anything which has MASS!
• Note that MASS and WEIGHT are NOT the same thing!!!
what is mass?
Something with mass weighs something, and takes up VOLUME. Mass is CONSTANT.
what did the greeks focus on?
450 B.C. The Greeks did not have the capability, or desire to do any complicated EXPERIMENTS, so they focused on what happens on the SURFACE of MATTER.
what did empedocles say
A philosopher by the name of EMPEDOCLES proposed that matter was
made of FOUR ELEMENTS: EARTH, WATER, AIR, FIRE
what did empedocles think happened when you mixed elements?
He thought that if you MIXED these elements together in DIFFERENT AMOUNTS, you would make DIFFERENT SUBSTANCES.
what example did empedocles use
• When you burn wood you see FIRE.
• When you leave wood alone it DRIES OUT, so there must be WATER present.
• AFTER it is BURNED, ASHES are left (EARTH).
• While it burns, SMOKE is released (AIR)
what did democritus think
400 B.C. Democritus
• Suggested that MATTER was made up of tiny PARTICLES, which couldn’t be BROKEN DOWN any farther.
• He called these particles ATOMS, from the Greek word ATMOS meaning INDIVISIBLE.
• He also thought that DIFFERENT TYPES of MATTER were made of DIFFERENT KINDS of ATOMS.
why was democritus's idea not accepted?
because SOCRATES didn’t believe it was true.
who was aristotle and who did he believe?
• Aristotle was a very well respected scholar and philosopher who organized much of the scientific knowledge at the time.
• He believed EMPEDOCLES’ theory about the FOUR ELEMENTS, and because he had such an INFLUENCE, this model, and many other theories were accepted for about 2000 YEARS.
what did aristotle come up with
Aristotle also came up with a theory called TRANSMUTATION: One form of matter could be turned into another. This was particularly exciting to the Greeks, since if it were true you could turn something WORTHLESS (say LEAD) into GOLD. This paved the way for the ALCHEMISTS.
who were alchemists?
• The Alchemists were the first people to perform experiments. (500-1600BC)
what were the alchemist's goals?
• Change base metals (tin, lead) into valuable gold.
• Find the substance for eternal life.
• Produce a universal solvent to dissolve all substances.
were the alchemists goals ever reached?
no
why are the alchemists important?
• discovered many elements and their properties, and created
chemical symbols for them.
• invented many lab tools that we still use today. (beakers,
filters, distillation apparatus, etc.)
• actually performed experiments.
who were the modern chemists?
Sir Frances Bacon (1561‐1626), Robert Boyle (1627‐1691), Joseph Priestly (late 1700’s), Antoine Lavoisier (1743‐1794).
Sir Frances Bacon (1561‐1626) (#)
1
• New knowledge must be based on experimentation, and not speculation
• Experiments must be repeatable.
Robert Boyle (1627‐1691) (#)
2
• Did not believe the four‐element theory.
• Showed that substances could be mixed to form compounds
Joseph Priestly (late 1700’s) (#)
3
• Was the first person to isolate oxygen scientifically
Antoine Lavoisier (1743‐1794) (#)
4
• Discovered over 23 different elements
• Determined air is made of oxygen and other gases.
• Was guillotined in the reign of terror
what is an element?
a pure substance that cannot chemically be broken down into simpler substances.
example of substances being broken down into elements
WATER can be broken down into HYDROGEN and OXYGEN,
which are ELEMENTS that CANNOT be broken down any
further.
when was it accepted that matter was made of elements?
By 1808, it was widely accepted that matter was made up of ELEMENTS, which consisted of tiny PARTICLES called ATOMS. After 2000 years - DEMOCRITUS was right all along
john dalton (1766-1844)
Dalton came up with one of the first models for what atoms look like
Dalton’s Atomic Theory
• All elements are made of atoms.
• Atoms are indestructible.
• Atoms of the same element are exactly alike
• Two or more elements combine to form compounds.
• Atoms are not created or destroyed in a chemical reaction.
what is another name for daltons atomic theory
Dalton’s atomic theory is also known as the “BILLIARD BALL MODEL” since he believed that atoms were just tiny SPHERES. it would look like a magic 8 ball
Joseph John (J.J.) Thompson (1904) what did he do
Thompson was passing ELECTRICITY through a GAS, when he discovered very LIGHT, NEGATIVE PARTICLES that he called ELECTRONS, DISPROVING Dalton’s theory that the atom is INDIVISIBLE. Later he also discovered HEAVIER, POSITIVE PARTICLES called PROTONS.
what did thompon propose?
• Electrons have small mass and a negative charge.
• An atom is a sphere of positive electricity.
• Electrons stuck in the positive sphere.
another name for thomspons theory
Thompson’s theory is also called the “RAISIN BUN” or “PLUM PUDDING” or “BLUEBERRY MUFFIN” model. it would look like a chocolate chip cookie
Ernest Rutherford (1911) what did he do
Performed a famous experiment where “SHOT” a beam of ALPHA PARTICLES at a sheet of GOLD FOIL (the gold foil experiment).He found that MOST of the PARTICLES went THROUGH the foil, as if it were made of EMPTY SPACE, while some BOUNCED off. Through this experiment he discovered a DENSE, POSITIVELY charged NUCLEUS.
what did rutherford propose
• The nucleus is a tiny, dense, positively charged core
• Protons are in the nucleus
• The nucleus is surrounded by mostly empty space.
• Electrons are moving outside the nucleus in an electron cloud.
what is rutherfords model called
nuclear model (LOOK UP A PIC AND REMEMBER IT)
Neils Bohr (1913) what did he do
Bohr thought that if RUTHERFORD’S theory were true, the ELECTRONS would just CRASH into the NUCLEUS (since OPPOSITE charges ATTRACT) He used the idea of planets orbiting the sun to improve upon Rutherford’s model of the atom
what did bohr propose
• Electrons move around the nucleus in orbits (like planets around the sun).
• Each orbit is an energy level – Higher orbits have more energy.
• Electrons cannot exist between orbits
• Electrons are more stable at lower energy levels.
• The order of filling electrons is 2-8-8.
what is bohrs model called
His theory is also called the “PLANETARY MODEL”. (LOOK UP A PIC AND MEMORIZE IT)
Quantum Model of the Atom
Bohr’s model works well for SIMPLE ATOMS (eg, H), but does not explain more complicated ones.
The quantum model says that instead of circular paths around the nucleus, the orbits are more like “CLOUDS” where electrons can be found. (more on this in grade 12)
what is an atom made of
Today we know that an atom is made up of three major SUBATOMIC particles
• protons (+ve)
• electrons (-ve)
• neutrons (neutral)
subatomic particle characteristics
Subatomic Particle- proton, neutron, electron
Symbol & Charge- p+ n0, e-
Mass- 1 amu, 1 amu, 1/1837 amu
Location- nucleus, nucleus, electron shell
compare electron to p&n
The mass of an ELECTRON is almost 2000X LESS than a PROTON or NEUTRON.
what are elements made of
identical atoms
What does the atomic number represent?
The atomic number represents the number of protons in an atom's nucleus. ex) Carbon-Atomic number = 6 so it has 6 PROTONS
What does the atomic mass (mass number) represent?
The atomic mass represents the total of the number of protons and neutrons in an atom's nucleus. (# of p+) + (# of n0) = atomic mass
Standard Notation
Shows an elements SYMBOL, atomic MASS, and atomic NUMBER: C 12 -atomic mass
6 -mass number
neutral atom
If the atom is NEUTRAL (SAME # of POSITIVES as NEGATIVES), the # of PROTONS and ELECTRONS will be EQUAL.
How do you calculate the number of neutrons in an atom?
Subtract the atomic number from the atomic mass.
what does a bohr diagram show
- the arrangement of ELECTRONS OUTSIDE the NUCLEUS
- number of PROTONS and NEUTRONS in the NUCLEUS.
- The number of VALENCE ELECTRONS
rules for drawing bohr diagrams
e- in orbitals
p + n in nucleus (say how many)
nucleus is solid line, orbitals are dotted lines
1862 ‐ A.E. Beguyer de Chancourtois
Listed the elements positioned on a cylinder in terms of ATOMIC WEIGHT and noticed that elements with similar PROPERTIES lined up.
1864 – John Newlands
Law of OCTAVES which stated that elements REPEATED their chemical properties every EIGHTH element
1868 – Lothar Meyer
First to recognize a REPEATING pattern of PROPERTIES when elements were organized by MASS
1869 ‐ Dimitri Mendeleev
He also arranged the 63 known elements in order of their ATOMIC MASSES and also saw the repeating pattern of properties. Not all of the elements had been discovered at that time, so Mendeleev left SPACES for UNDISCOVERED elements, CORRECTLY PREDICTING that elements would be found to FILL the SPACES.
Henry Mosely (1901)
Found that PHYSICAL and CHEMICAL PROPERTIES are related to their ATOMIC NUMBER (# protons) not ATOMIC MASS. Created the MODERN periodic table in which each element has ONE MORE PROTON and ELECTRON than the one before it. When elements are arranged this way, the REPEATING PATTERN of similar properties is called the PERIODIC LAW. Today we know that it is the ELECTRON that determines the PROPERTIES of an ELEMENT, and the NUMBER of ELECTRONS is related to the ATOMIC NUMBER, not ATOMIC MASS.
how periodic table is organized
Periods:
• HORIZONTAL ROWS on the periodic table, with the numbering system 1‐7 from TOP to BOTTOM of the periodic table.
• Each PERIOD represents an ENERGY LEVEL (ELECTRON SHELL)
how the periodic table is organized groups
Groups/Families:
• VERTICAL COLUMNS on the periodic table.
• Labelled 1‐18
• elements with SIMILAR CHEMICAL PROPERTIES.
• Elements in a GROUP all have the SAME NUMBER of VALENCE ELECTRONS.
• The number of VALENCE ELECTRONS is the same as the group number – kind of.
Families of the Periodic Table...
The elements in a column (Family) on the periodic table BEHAVE in a SIMILAR way, just like with human families. There are 6 families we need to look at
family hydrogen
1. Hydrogen (in it’s own family):
• Has 1 VALENCE ELECTRON.
• REACTS VIGOROUSLY, and is highly EXPLOSIVE.
• Cannot exist as a SINGLE ATOM, but as a MOLECULE (H2).
family alkali metals
2. Alkali Metals (group 1):
• Contains: Li, Na, K, etc.
• REACT very VIGOROUSLY with many other substances.
• The LARGER the Alkali Metal, the MORE REACTIVE it is.
• Have only 1 VALENCE ELECTRON.
family alkaline metals
3. Alkaline Earth Metals (Group 2)
• Contains: Be, Mg, Ca, etc.
• React FAIRLY VIGOROUSLY, but not AS MUCH as the ALKALI METALS.
• LARGER the Earth Metal, the MORE REACTIVE it is.
• Are similar in STRUCTURE to the ALKALI METALS, but have 2 VALENCE ELECTRONS.
family chalcogens
4. Chalcogens (Group 16):
• Contains: O, S, Se, etc.
• QUITE REACTIVE, not as reactive as HALOGENS.
• Have similar STRUCTURE to HALOGENS, but have only 6 VALENCE ELECTRONS.
family halogens
5. Halogens (Group 17):
• Contains: F, Cl, Br, I, etc.
• React VERY VIGOROUSLY with nearly everything.
• Least reactive are still very CORROSIVE.
• The LARGER the atom, the LESS REACTIVE.
• Have 7 VALENCE ELECTRONS.
family noble gases
6. Noble Gasses (group 18):
• Contains: He, Ne, Ar, etc.
• Are very UNREACTIVE.
• Have a FULL VALENCE SHELL (8 ELECTRONS).
How does the number of valence electrons relate to reactivity?
the closer to filling the valence shell, the more reactive
Ductility
The ability to be shaped or stretched into a wire without breaking.
Malleability
The ability to be hammered, pressed, or rolled into thin plates.
Conductivity
How easily heat and electricity can pass through a substance.
Lustre
How shiny or dull a material is
what are the three major areas the families fall into?
metals, non metals, metalloids.
Metals
• Make up about 75% of all the elements.
• They are located all over the periodic table, but are CONCENTRATED at the LEFT SIDE.
• Metals are SHINY. They CONDUCT HEAT, and can make WIRES or be stretched into SHEETS.
Non-Metals
• Make up about 15% of the elements. They are found at the FAR-RIGHT side of the periodic table.
• Are POOR CONDUCTORS, are NOT SHINY, and are BRITTLE and NOT DUCTILE.
metal examples
copper lead tin
non metal examples
carbon iodine sulphur
Metalloids
• Make up about 6% of the elements. They are found on the “STAIRCASE” of the periodic table.
• They have properties of BOTH METALS and NON METALS.
metalloids example
boron silicon arsenic
metals, non metals, metalloids properties
METALS: Mostly solids at room temperature (except Hg)Shiny lustre, Good conductors, Malleable, Ductile
NON METALS: Some gasses, some solids At room temp. (Br is liquid), Dull (Not shiny), Poor conductors, Brittle, Not Ductile
METALLOIDS: Solids at room temperature, Can be shiny or dull, May conduct electricity (Poor conductors of heat), Brittle, Not Ductile
Physical Properties:
- Are CHARACTERISTICS or DESCRIPTIONS of a SUBSTANCE that may help to IDENTIFY it.
- Are usually EXTERNAL OBSERVATIONS like TOUCH, SIGHT, SMELL etc.
- Do NOT involve the substance becoming a NEW SUBSTANCE.
physical properties examples
Colour, Lustre, Malleability, Ductility, Magnetism, Melting point,
Boiling Point, Solibility, Conductivity
Chemical Properties
- Describe the BEHAVIOUR of a substance as it BECOMES a NEW SUBSTANCE.
- Are the WAYS in which different substances REACT with eachother.
chemical properties examples
Flammable, Reacts with acids/bases, Corrosive
what does chemical reactivity depend on?
it depends on the number of ELECTRONS that are in the VALENCE SHELL.
what do all atoms want?
All ATOMS want to become STRUCTURALLY and CHEMICALLY STABLE. This means that they want to be UNREACTIVE like the NOBLE GASES (have FULL OUTER SHELLS). An atom must obtain a FULL OUTER SHELL in order to become STABLE and UNREACTIVE.
To get a full outer shell an atom can:
1. Gain electons
2. Lose electrons
3. Share electrons
Of these three, an atom will do whatever is EASIEST. (if it has 1 VALENCE ELECTRON, its easier to LOSE the 1 electron than it is to FIND 7 MORE)
metals / non metals: losers vs gainers
metals: losers
non metals: gainers
explain physical changes
- When a substance undergoes a CHANGE in FORM, SHAPE or STATE.
- The substance is STILL the SAME after a PHYSICAL CHANGE.
Nothing new is made!
Examples:
• Tearing a piece of paper
• Melting ice cream
• Dissolving sugar
explain chemical changes
- The substance is changed into ONE or MORE DIFFERENT SUBSTANCES with DIFFERENT PROPERTIES.
- The ATOMS are the SAME, but they are REARRANGED into DIFFERENT MOLECULES.
- The PRODUCTS are DIFFERENT than the REACTANTS.
Something new is made!
Examples:
• A car rusts
• Wood burns
signs of a chemical change
1. BUBBLES
2. PRECIPITATE FORMS
3. COLOUR CHANGE
4. LIGHT IS EMITTED
5. VOLUME CHANGE
6. TEMPERATURE CHANGE
7. CHANGE IN CONDUCTIVITY
8. BOILING POINT/MELTING POINT CHANGE
9. CHANGE IN SMELL OR TASTE
10.CHANGE IN DISTINCT CHEMICAL PROPERTIES
Atom:
- Smallest UNIT of an ELEMENT.
- Made of PROTONS, ELECTRONS and NEUTRONS
Molecule
- Is a PURE SUBSTANCE made of a CLUSTER of atoms of SIMILAR or DIFFERENT ELEMENTS.
- Can be BROKEN DOWN into those ATOMS during a CHEMICAL CHANGE.
Compound
- A PURE SUBSTACNCE whose MOLECULES are made of DIFFERENT KINDS of ATOMS.
- COMPOUNDS can be broken down into DIFFERENT ELEMENTS.
A PURE SUBSTANCE
is something that contains only ONE KIND of MATTER.
A MIXTURE
is something that contains TWO or MORE PURE SUBSTANCES.
how many pure substances are there
There are about 10 million known PURE SUBSTANCES
- Only about 112 of these are actually ELEMENTS, the rest are compounds or molecules
compound example
Baking soda is actually SODIUM BICARBONATE (NaHCO3)
A mixture of SODIUM, CARBON and OXYGEN atoms. It is a COMPOUND or a MOLECULE
what is pure oxygen
Pure OXYGEN is just O2, It is a MOLECULE AND an ELEMENT.
Chemical Formula
The combination of CHEMICAL SYMBOLS that show:
- What ELEMENTS make up a CHEMICAL COMPOUND.
- How many ATOMS of EACH ELEMENT there are.
the chemical formula for water is H2O.
- The letter H stands for HYDROGEN.
- The letter O stands for OXYGEN.
- The 2 tells you that there are 2 ATOMS of HYDROGEN.
- There is a 1 UNDERSTOOD after the O.
Rules for Counting Atoms (symbols)
1. Symbols:
- Each CAPITOL letter means that there is a NEW ELEMENT
Ex) Li2Cl3 is made of LITHIUM and CHLORINE
Na2SO4 is made of SODIUM, SULPHUR and OXYGEN
Rules for Counting Atoms (subscripts)
Subscripts:
- A NUMBER that comes after a SYMBOL and BELOW.
- The subscript only affects the element it COMES AFTER.
Ex) Li2Cl3 Has 2 LITHIUM ATOMS and 3 CHLORINE ATOMS
rules for counting atoms (brackets)
- A SUBSCRIPT OUTSIDE a bracket affects ALL the elements INSIDE the bracket...(ie. MULTIPLY!!!)
Ex) Al(SO4)3 Has 1 ALUMINUM atom, 3 SULPHUR atoms and 12 OXYGEN atoms there’s 3 of everything in the brackets!
rules for counting atoms (coefficients)
- A “FULL SIZE” number in FRONT of a chemical FORMULA.
- MULTIPLIES everything in the formula: Ex) 2Na2SO4 Has 4 SODIUM atom, 2 SULPHUR atoms and 4 OXYGEN atoms
what is a lewis dot diagram
represents the number of valence electrons (look at the picture) arranged in a square