1. 8th Grade Science-Atoms Unit
Properties of Atoms and the Periodic Table

2. Structure of the Atom Chemical Symbols-
consist of one capital letter or a capital letter plus one or two small letters
ex: table 1—pg. 544

3. Atomic Components
Atoms—the smallest piece of matter that still retains the property of the element
Atoms: Contain protons and neutrons in the nucleus
Electrons—contained in electron cloud

4. Quarks—smaller particles that comprise protons and neutrons
Scientists have confirmed the existence of six uniquely different quarks
The search for the composition of protons and neutrons is an ongoing effort

5. Atomic Theory-Past Models of the Atom
Democritus—around 400 BCE
composed of tiny, solid particles that could not be subdivided/cut apart further
Called these particles”atomos”
(did not conduct experiments as proof)

6. Dalton—solid sphere model (pool ball)--
1808--Dalton proposed an ATOMIC THEORY with 3 main points--
All matter is made up of atoms
Atoms cannot be created or destroyed
All atoms of a certain element are identical, of they are different from atoms of all other elements

7. JJ Thomson—(1897)conducted experiments providing evidence that atoms are made up of even smaller particles with a negative charge—ELECTRONS
-known as “plum pudding” or cookie dough model w/electrons embedded in positively charged sphere

8. Ernest Rutherford—(1909)
-conducted the “gold foil” experiment
-suggested atoms have a nucleus—positive center surrounded by moving electrons
-he called the positively charged particles in the nucleus--PROTONS

9. Niels Bohr—(1913)
--Hypothesized about electrons traveling in fixed orbits
-The Bohr model shows electrons moving around the nucleus in circular paths a certain distance from the nucleus
-This model helped to predict properties of elements
-(This is the model we see drawn most often)

10. Electron Cloud Model
(1926)—current model (due to discovery of neutrons in nucleus as well)
Electron cloud—area around the nucleus of an atom where its electrons are most likely found (cannot be predicted)
Energy levels are areas of the cloud where electrons are more likely to be found

11. Masses of Atoms AMU—unit of measurement used for atomic particles
Mass of 1 proton or 1 neutron is almost 1 amu.
Atomic number—the number of protons in an atom
Mass number—the sum of the number of protons and the number of neutrons in the nucleus

12. Atomic mass = decimal number under the symbol on the periodic table
NOT THE SAME THING AS ATOMIC NUMBER or MASS NUMBER
It is the average weight of all atoms of the element (including isotopes)

13. Calculating neutron number
If you know the mass number and atomic number of an atom, you can find the number of neutrons as well,.
Neutron # = mass # atomic #

14. Isotopes Carbon-12 is the most common form of carbon
However, Carbon-14 is a radioactive form of carbon
WHY?
Not all the atoms of an element have the same number of neutrons

15. ISOTOPES
Isotopes—atoms of the same element that have different numbers of neutrons
Average atomic mass—the weighted average mass of an element’s mixture of isotopes (used because most elements have more than one isotope)

16. The Periodic Table
Dimitri Mendeleev-arranged all the elements known in order of increasing atomic masses and discovered a pattern
Today’s Periodic Table—elements are arranged by increasing atomic number and by changes in physical and chemical properties

17. Mendeleev-left blank spaces to keep elements in line according to chemical properties
He predicted the existence of two elements not yet discovered

18. Groups
The vertical columns in the periodic table-also called families
Periodic Table—pg. 556 and 557

19. Electron Cloud Structure
In neutral atoms, the electron number = the proton number
SO: Atomic number tells how many protons AND how many electrons the element has

20. Elements in the same group have the same number of electrons in their outer energy level-called VALENCE ELECTRONS
This number determines properties of the elements

21. Number of Atoms in Energy Levels
Energy Level 1—holds 2 e
Energy Level 2—holds 8 e
Energy Level 3—holds 18 e
Energy Level 4—holds 32 e
Octet Rule—explains that atoms are most stable with an outer valence holding 8 electrons

22. Periods/Rows Horizontal groups across the periodic table
Each row ends with an element with a full outer valence (8 electrons)
Periods increase by one proton and one electron going L to R

23. Metals Metals are on the left-hand side of the periodic table
Most are shiny, ductile, malleable and are good conductors
Ductile—drawn into wire
Malleable-can be hammered into sheets

24. Non-metals Non-metals are on the right side of the periodic table
Most are gases, brittle, and poor conductors

25. Metalloids Metalloids-run along the middle zig-zag line
Metalloids have some of the properties of both metals and non-metals

26. Carbon-14
has 6 protons and 8 neutrons
Isotopes—atoms of the same element that have different numbers of neutrons
Radioactive isotopes—those isotopes that are unstable and become radioactive

27. Identifying Isotopes
Average atomic mass—the weighted-average mass of the mixture of its isotopes
Ex: 4 out of 5 atoms of B are boron-11 and 1 out of five is boron-10
Weighted average =
4/5 (11) + 1/5(10) = 10.8 AMU

28. Periodic Table websites: