Chem
What is MATTER?
Note that MASS and WEIGHT are NOT the same thing!!!
What did Empedocles (450 bc) theorize?
proposed that matter was made of FOUR ELEMENTS: earth, water, air, fire
What did Democritus 400 BC believe?
Suggested that MATTER was made up of tiny PARTICLES, which couldn’t be BROKEN DOWN any farther.
He also thought that DIFFERENT TYPES of MATTER were made of DIFFERENT KINDS of ATOMS.
why want democritus believed?
because Socrates didn't believe it was true
What did Aristotle believe?
He believed EMPEDOCLES’ theory about the FOUR ELEMENTS + he believed in transmutation (that one form of matter could be turned into another)
who were the alchemists?
The Alchemists were the first people to perform experiments.
what were the alchemists' goals?
• Change base metals (tin, lead) into valuable gold.
• Find the substance for eternal life.
• Produce a universal solvent to dissolve all substances.
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 is Sir Frances Bacon (1561‐1626)?
(1561‐1626)
• New knowledge must be based on experimentation, and not speculation
• Experiments must be repeatable.
Robert Boyle
(1627‐1691)
• Did not believe the four‐element theory.
• Showed that substances could be mixed to form compounds
Joseph Priestly
(late 1700’s)
• Was the first person to isolate oxygen scientifically
Antoine Lavoisier
(1743‐1794)
• 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.
what was john daltons model?
Dalton’s atomic theory is also known as the “BILLIARD BALL MODEL”
,
since he believed that atoms were just tiny SPHERES.
Joseph John (J.J.) Thompson (1904)?
- discovered the electron
- Thompson’s theory is also called the “RAISIN BUN” or “PLUM
PUDDING” or “BLUEBERRY MUFFIN” model: it has a sphere of positive charge with negative particles inside
Ernest Rutherford 1911
he discovered a DENSE, POSITIVELY charged
NUCLEUS.
Rutherford developed what we call the NUCLEAR MODEL
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.
Niels Bohr
He proposed that:
• 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.
Atomic Number
The NUMBER of PROTONS in the NUCLEUS of an atom
Atomic Mass
The AVERAGE MASS of an atom of an element / Is the TOTAL of the NUMBER of NEUTRONS and PROTONS in the
NUCLEUS of an atom.
1864 – John Newlands
Law of OCTAVES which stated that elements REPEATED their chemical
properties every EIGHTH element
1868 – Lothar Meyer
recognised a pattern when elements were organised 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.
Mendeleev left empty spaces for undiscovered elements.
what are the features of the current periodic table?
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)
what are the qualities of non-metals?
non shiny, not malleable, not ductile, poor conductor
what are the qualities of metals?
shiny lustre, very malleable, ductile, good conductor, solid at room temp (except mercury)
what are the qualities of metalloids?
shiny or dull, poor conductors, brittle, not ductile, solid at room temp
metals make up ___ of the periodic table
75%
non-metals make up ___ of the periodic table
15%
metalloids make up ___ of the periodic table
6%
what are the signs of a chemical change?
1. BUBBLES
2. PRECIPITATE FORMS
4. LIGHT IS EMITTED
6. TEMPERATURE CHANGE
10.CHANGE IN DISTINCT CHEMICAL PROPERTIES