Atoms, Elements, and Compounds

Chapter 1, Unit E Vocabulary Lesson 1

1. atom - the smallest unit of a pure substance

2. nucleus - center of the atom; positive charge, made up of at least one subatomic particle and usually several that are close together

3. proton - subatomic particle w/positive electric charge; part of nucleus; same mass as neutron (1)

4. neutron - subatomic particle w/neutral electric charge; part of nucleus; same mass as proton (1)

5. electron - subatomic particle w/negative charge; constant motion around nucleus in a “cloud”; mass less than proton and neutron

6. atomic number - the number of protons in an atom

I. DemocritusA. 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.”

II. John DaltonA. English chemist, early 1800’s1. 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

III. J.J. ThomsonA. late 1800’sB. made a model of an

atom to show that atoms are made of subatomic particles

IV. Ernest RutherfordA. model suggested

the atom is made up of mainly of empty space

B. electrons spaced around the dense central nucleus

I. Ernest Rutherford’s ExperimentA. In 1911 Rutherford created

an experiment that demonstrated that the atom has a nucleus

B. the atom is made up of alot empty space

C. nucleus - 99.9% of atom’s mass

D. proton and neutron - 2000 times the mass of an electron

I. 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

I. 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

1. atom is the smallest unit of a substance that still has the properties of that substance

2. nucleus of an atom contains protons and neutrons and is surrounded by electrons

3. atoms of different substances have different number of protons

4. atoms of the same substance but with different number of neutrons are isotopes

5. protons are positive, electrons are negative6. neutral atoms have the same number of protons and

electrons

2. 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.

1. What are the subatomic particles that make up an atom?

The subatomic particles that make up an atom are protons, neutrons, and electrons.

1. 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.2. Which of the subatomic particles is the

smallest?The smallest subatomic particle is the electron.

3. What are isotopes?

Isotopes are atoms that have the same number of protons, but different number of neutrons.4. 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.5. Which of the following is not a subatomic

particle?B. ion