1. Ch 7. Understanding the atom & Ch 8. elements and chemical bonds
KMS 8th grade science

2. The atom
The smallest piece of an element that still represents that element.
The atom is made up of main parts
two
Electron Cloud
Nucleus

3. The nucleus A small area in the center of an atom
Responsible for most of the atom’s mass
Contains positive charge
Contained in the nucleus:
protons
neutrons

4. PRotons An atomic particle that has a positive charge Size: Charge:
Location:
Atomic Mass Unit (amu) =
Larger than electrons
Positive
Nucleus
1 amu

5. Neutrons Neutral particle that exists in the nucleus of an atom. Size:
Charge:
Location:
Atomic Mass Unit (amu) =
Larger than electrons (about the same size as a proton)
Neutral
Nucleus
1 amu

6. The electron cloud
The area around an atomic nucleus where an electron is most likely to be located
Contained in the electron cloud:
electrons

7. electrons A particle with a negative charge. Size: Charge: Location:
Atomic Mass Unit (amu) =
Much smaller than protons and neutrons
Negative
Electron Cloud
1/1,840 amu

9. Contributors Democritus (pg. 236) Aristotle (pg. 236)
John Dalton (pg. 236)
J.J. Thomson (pg. 238)
Ernest Rutherford (pg. 240)
James Chadwick (pg. 245)
Niels Bohr (pg. 245)

10. Democritus
Proposed that different types of matter are made from different types of atoms.
Proposed that space between atoms was “empty”

11. Aristotle
384 – 322 B.C.
Did not believe in Democritus’ idea that between atom’s were empty space
He believed all matter was made of fire, water, air and earth.

12. John dalton
Late 1700’s
All matter is made of atoms that cannot be created, divided or destroyed.
Atoms of the same element have the same mass and are exactly alike

13. j.j. thomson
1897
Found negatively charged particles (electrons) and reasoned that they must have a positive charge that balances them out.

14. Ernest Rutherford Thomson’s student First atomic model with nucleus
Came up with the word proton for positive charge

15. James chadwick
Discovered the neutron
Completed the atomic model

16. Niels bohr
Proposed that electrons move in circular orbits, called energy levels, around the nucleus.

17. elements Pure substance made of only one type of atom
A substance made from atoms that all have the same number of protons.
In the empty box in your notes, look at
the periodic table and fill out an element
box for carbon

18. C Carbon element box Element Atomic Number Carbon 6 Symbol Atomic Mass
12.01

19. Atomic number The number of protons located in the atom’s nucleus.
Turn to the periodic table in your text book…can you find the atomic number in the following element boxes?
Oxygen
Potassium
Gold

20. Protons and neutrons The number of of the same element will always be
However, atoms of the same element can have
For example: every carbon atom has 6 protons, however some have 6, 7, or 8 neutrons.
protons
the same
a different number of neutrons

21. These are called…
Isotopes - atoms of the same element that have different numbers of neutrons.
Most elements have isotopes.
several

22. Mass number Average atomic mass
The sum of protons and neutrons in an atom.
Average atomic mass
The average mass of the element’s isotopes, weighted according to the abundance of each isotope.

23. The average atomic mass is and based on each isotope’s
Approximately 99% of Earth’s carbon is which is why carbon’s average atomic mass is close to 12 (12.01)
weighted
abundance on Earth
Carbon-12

24. The arrangement of elements
Arranged by:
Arranged in order of:
Periodic-
Dmitri Mendeleev ( )
Increasing atomic mass
Describes something that occurs or repeats in regular intervals.

25. The three main regions of elements on the periodic table classify elements as
Metals, nonmetals, or metalloids

26. Columns The (up and down) columns of the periodic table are called
There are groups
Elements in the same group or family have
vertical
groups or families 18
Similar chemical and physical properties

27. Rows The horizontal rows of the periodic table are called
Elements in a period
The first element in a period is usually an active , and the last element in a period is always an inactive .
periods
are not alike in properties
solid
gas

28. Rows Atomic number (number of protons)
Atomic mass (number of protons + neutrons)
Metals are on the
Non-metals are on the
increases from left to right across a period
increases from left to right across a
period
left
right

29. Energy levels Different electrons within an atom have
An electron moves around the nucleus at a distance that corresponds to
Electrons to the nucleus have the amount of energy.
Electrons from the nucleus have the energy.
different amounts of energy
the amount of energy it has.
closest
least
furthest
most

30. Electron Energy Levels

31. Energy levels
Negatively charged are strongly attracted to charged nucleus of an atom.
These OUTERMOST electrons can easily be attracted to the nucleus of
We call these OUTERMOST electrons
electrons
positively
other atoms
valence electrons

32. Energy levels
Valence Electrons - outermost electron of an atom that participates in chemical bonding.
These attractions are what cause
chemical bonds

33. How to determine the number of valence electrons
The number of in each atom of an element can help determine
The exception to finding number of valence electrons is
valence electrons
the type and the number of bonds it can form
helium

34. Group #/Valence electron
Helium is the exception and has V.E.
1 valence electron
2 valence electron
valence electrons vary
3 valence electrons
4 valence electrons
5 valence electrons
6 valence electrons
7 valence electrons
8 valence electrons 2
**go back to the periodic table in your notes and label the valence electrons.