1. Atoms and the Periodic Table

2. Matter Matter is everything around you that has mass.
Anything you can see, touch, taste, or smell is matter!
Air
Desks
People
Soil
Plants
What is it that makes up matter?!

3. Matter What is matter made of? Is it all the same?
Democritus (460 B.C B.C.) was a Greek philosopher believed the universe was mostly empty space and tiny bits of stuff.
He didn’t know what the stuff was but he knew it must be REALLY small!
So small it could not be broken into anything smaller

4. The Chalk Conundrum!
If you break a piece of chalk in half…is it still chalk?
When is it no longer chalk?

5. Can you make matter?
Democritus never explained where matter came from or where it could go
People just guessed that matter could change into different types of matter

6. Matter cannot be created or destroyed!
Can you make matter?
Matter cannot be created or destroyed!
If a space shuttle leaves Earth with astronauts and food and water and air weighing 10,000 lbs. it will return weighing 10,000 lbs.

7. Matter Atom – small particle that makes up matter
Atom in Greek means “cannot be divided”

8. Parts of an Atom Protons – positive charged particle
Atoms are made of only 3 different things
Protons – positive charged particle
Neutrons – particle with no charge
Electrons – negatively charged particle
Nucleus – center of the atom made up of protons and neutrons
Protons and neutrons are found in the nucleus or center of the atom
Electrons are found outside the nucleus

9. Parts of an Atom
Electrons are so small as it is we hypothesize that they aren’t made up of anything smaller
Protons and neutrons however…
Quarks – smaller particles that compose protons and neutrons of an atom
6 unique quarks have been discovered
It took almost 450 scientists several years to discover the 6th quark!

10. How big are Atoms?
SMALL! Really, really, really, really, small…

12. The Atomic Model So what exactly does an atom look like?!
Scientists have developed models over the years to explain how atoms work…

14. Gold Foil Experiment
Rutherford was one of the first to propose that atoms had a dense nucleus
Gold foil experiment
Particles were fired at a piece of gold foil
Most went straight through
Some were deflected

16. Electron Cloud Model
By 1926, scientists had developed the electron cloud model of the atom
Electrons do not follow fixed orbits
Instead they occur frequently in certain areas around the nucleus at any given time

17. What is in an Atom?

18. Bohr Model Orbital – each ring of electrons in an atom
The Bohr model represents an atom by using rings drawn around the nucleus with dots to represent electrons
Orbital – each ring of electrons in an atom
The 1st orbital can only hold 2 electrons!
The following orbitals can only hold a maximum of 8 electrons

19. Atoms
Element – a known substance that cannot be broken down into another substance
Made of only one kind of atom
Sulphur (S)
Potassium (K)
Aluminum (Al)
Chlorine (Cl)

20. Periodic Table
Periodic Table – a chart that organizes elements by the number of protons they have in the nucleus
Elements are listed by their chemical symbols
Aluminum = Al
Calcium = Ca
Gold = Au
Oxygen = O
Hydrogen = H
Carbon = C

22. How to Read a Periodic Table
Dimitri Mendeleev, a Russian Chemist, developed the first periodic table
Mendeleev based his table on the mass of the atoms
“I began to look about and write down the elements with their atomic weights and typical properties, analogous elements and like atomic weights on separate cards, and this soon convinced me that the properties of elements are in periodic dependence upon their atomic weights.”
A British chemist later improved upon the periodic table by rearranging the elements based on their atomic number (the number of protons).

23. Atomic Number
Atomic number – the number of protons found in a single atom of the element
The periodic table is arranged based on these numbers

24. Atomic Mass
If you were asked how tall you were, would you answer in kilometers?
NO! You would use an appropriate unit! (cm, or m)
Scientists had to develop an appropriate unit for the mass of atoms since they were so tiny!
Atomic mass unit (amu) – unit of measure used for atomic particles
Atomic mass – the mass of an atom of the element

25. Atomic Mass How do we calculate the atomic mass?
1 proton is equal to almost exactly 1 amu
1 neutron is equal to almost exactly 1 amu
Electrons are so tiny they make little difference

26. How Many Neutrons?
The number of protons in an atom is equal to the element’s atomic number
The number of electrons in a neutral atom are equal to the number of protons
1 positive and 1 negative equals 0!
Often, the number of neutrons is equal to the number of protons but NOT ALWAYS!

27. How Many Neutrons? Krypton Has an atomic number of 36
Number of protons?
Number of electrons?
Number of neutrons?
Round the atomic mass to the nearest whole number
83.80  84
84 – 36 protons = 48 36 36

28. Reading a Periodic Table
All the rows read from LEFT to RIGHT
Each row is called a period
The period an element is in tells you how many electron orbitals are present
Elements in the top period have 1 orbital
Elements in the 3 period have 3 orbitals

29. Reading a Periodic Table
The vertical columns of the periodic table are called groups
Elements found in the same group have the same number of electrons in their outer orbital
Valence Electrons – the electron in the outermost ring of an atom
Elements in group 1 have 1 electron in their outer shell
Elements in group 4 have 4 electrons in their outer shell
The middle “transition elements” don’t follow this rule!
We’ll talk about them later on…

30. Try it! Nitrogen Atomic number? Number of protons? 7
Number of electrons?
Number of neutrons?
Atomic mass?
Number of valence electrons? 7 7 7 7 14 7