 What is an observation?  What is a theory? Observation – gathering information using senses Theory – explanation of observations that has been supported by repeated experimental results

 Models – a diagram, picture or 3-D structure to represent ideas  Scientists use models to explain ideas hard to explain or imagine like the atom.

 8000BC – Stone Age – fire was used to shape tools  4500 BC – Bronze Age – copper was heated with tin to create a new metal (strong)  1200BC – Iron Age – steel was produced by combining iron and carbon (stronger/sharper)

 500BC – Democritus – used word “atomos” to describe smallest unit of matter  -Atoms could be put together to make new matter with different properties

 350BC – Aristotle – believed matter was made from earth, air, fire and water.

 1600s – Alchemy – was a mixture of magic and science  -created Plaster of Paris  -Believed metals  gold

 1660s – Robert Boyle  -Studied gases and pressure  -Believed matter was made of particles  -These particles could combine to make new matter

 Antoine Laurent Lavoisier  Developed a system for naming chemicals ▪ “Father of Modern Chemistry”

 John Dalton  >Matter was made of elements  >Elements are pure substances of one atom  >Every atom in an element are identical  > Billiard Ball model

 J.J. Thomson  Created the “Raisin Bun Model”  Discovered first subatomic particle - the electron  Believed atoms were positive spheres with negative electrons embedded.

 Hantaro Nagaoka – believed the center of the atom was positive and electrons (negative) orbited the center

 Ernest Rutherford  -Atoms – mainly empty space with a tiny positive center (nucleus); electrons are randomly around it  Neils Bohr -believed electrons orbit around nucleus in energy levels  James Chadwick  -discovered the nucleus contained protons (+) and neutrons (no charge)

*The Atom *  Is the smallest unit of matter and is made of 3 subatomic particles: ▪ Electrons (-) orbit around the outside of the nucleus ▪ Protons (+) part of the nucleus ▪ Neutrons (o) part of the nucleus  Each element is made of an atom with a specific number of protons, neutrons and electrons  Is neutral – has same # of electrons as protons

 WHY do we learn about the history of chemistry?  What is the purpose of re-learning history?  What does history tell us about the nature of science?

 Is the arrangement of elements according to patterns in behavior  Was developed by Dmitri Mendeleev in 1880’s  His idea was based on patterns in melting points, density and color

 Arranged in the following patterns: 1) Metals/Non-metals -metals are left of staircase = * malleable, ductile and conductive -non-metals are right of staircase = * brittle and non-conductive -metalloids – are on staircase; have properties of both metals and non-metals

2) Periods – horizontal rows ># of protons increases as you go left to right >Left side are metals; right side are non-metals >The reactivity of metals decreases as you go right

 3) Groups / Families – vertical columns; similar properties within a group  Alkali Metals – most reactive metals; react with air and water  Alkali Earth Metals – less reactive metals  Halogens – most reactive non-metals;  Noble gases- Most stable and unreactive elements

ALKALIALKALI EARTH NOBLE GASES HALOGENS Increase in size, # of atomic particles  Increase in size, reactivity

 Atomic number – the number of protons  Since atoms are neutral, is also # of electrons  Atomic mass – the number of protons + neutrons To find # of neutrons: Atomic mass – atomic # = neutrons

 Ex. What is the symbol for aluminum? Iron?  What elements are in each of the following groups:  A) Alkali earth  B) Alkali  C) Halogens  D) Noble gases

 What is the atomic number of sodium?  Atomic mass? Number of protons, neutrons and electrons?  Is sulphur a metal or non-metal?  How many protons, neutrons and electrons does nitrogen have?