1. Atoms, Elements, and Compounds

2. Chapter 1, Unit E Vocabulary Lesson 1
atom - the smallest unit of a pure substance
nucleus - center of the atom; positive charge, made up of at least one subatomic particle and usually several that are close together
proton - subatomic particle w/positive electric charge; part of nucleus; same mass as neutron (1)
neutron - subatomic particle w/neutral electric charge; part of nucleus; same mass as proton (1)
electron - subatomic particle w/negative charge; constant motion around nucleus in a “cloud”; mass less than proton and neutron
atomic number - the number of protons in an atom

3. Matter is Made of Atoms Atom Timeline
Democritus
A. Greece 2400 years ago
B. Answered the question, “Suppose you could cut a piece of gold in half and then one of the smaller pieces in half. How many times could you keep cutting the pieces in half? What would you end up with?
Democritus suggested, “The tiny piece is called an atom.”

4. A. English chemist, early 1800’s
Timeline continued...
II. John Dalton
A. English chemist, early 1800’s
1. first scientist to use experiments to support atomic theory - theory that matter is made of atoms
2. hypothesized that atoms are the smallest particles of matter & they can’t be divided

5. Timeline continued...
III. J.J. Thomson
late 1800’s
made a model of an atom to show that atoms are made of subatomic particles

6. model suggested the atom is made up of mainly of empty space
Timeline continued...
IV. Ernest Rutherford
model suggested the atom is made up of mainly of empty space
electrons spaced around the dense central nucleus

7. Ernest Rutherford’s Experiment
The Nucleus
Ernest Rutherford’s Experiment
In 1911 Rutherford created an experiment that demonstrated that the atom has a nucleus
the atom is made up of alot empty space
nucleus % of atom’s mass
proton and neutron times the mass of an electron

8. can be thought of as different varieties of an element
Isotopes
All atoms of a substance have the same atomic number. But atoms of the same substance may have different masses - due to different number of neutrons.
can be thought of as different varieties of an element
isotopes of the same element behave the same way, but, have different structures

9. Charges In Atoms
The charges of subatomic particles have a great deal to do with the structure of an atom.
opposite charges attract, so the positive charge of the proton holds the negatively charged electrons in the cloud around the nucleus. Electrons closest to the nucleus are attracted more strongly than those farther away
opposite charges repel - so, why don’t protons “push away” from each other?...a strong nuclear force
when an electron is added or removed it changes the charge of the atom, the atom is then called an ion

10. atoms of different substances have different number of protons
Summary
atom is the smallest unit of a substance that still has the properties of that substance
nucleus of an atom contains protons and neutrons and is surrounded by electrons
atoms of different substances have different number of protons
atoms of the same substance but with different number of neutrons are isotopes
protons are positive, electrons are negative
neutral atoms have the same number of protons and electrons

11. What determines the atomic number of a substance?
Questions
What are the subatomic particles that make up an atom?
The subatomic particles that make up an atom are protons, neutrons, and electrons.
What determines the atomic number of a substance?
The number of protons in the nucleus of an atom of a substance determines the atomic number of a substance.

12. How are protons and neutrons alike, and how are they different?
Review Questions pg. E11
How are protons and neutrons alike, and how are they different?
Protons and neutrons are alike because both are in the nucleus, both have about same mass and size; they are different because protons have an electric charge, but neutrons do not.
Which of the subatomic particles is the smallest?
The smallest subatomic particle is the electron.

13. Review Questions pg. E11 continued...
What are isotopes?
Isotopes are atoms that have the same number of protons, but different number of neutrons.
If there a difference between a substance’s atomic number and atomic mass, which number must be the larger number?
The atomic mass must be the larger number.
Which of the following is not a subatomic particle?
B. ion