Chemistry Unit 1

History, Subatomic particles, isotopes, ions, etc

What is matter made of?

Matter is made of tiny particles called atoms.

What are the three main subatomic particles?

Protons, neutrons, and electrons.

What is the charge of a proton?

+1 (positive)

What is the symbol for a proton?

p⁺

Where is a proton located?

In the nucleus.

What is the relative mass of a proton?

About 1 amu.

What is the actual mass of a proton?

About 1.67 × 10⁻²⁴ g.

What is the charge of a neutron?

0 (neutral)

What is the symbol for a neutron?

n⁰

Where is a neutron located?

In the nucleus.

What is the relative mass of a neutron?

About 1 amu.

What is the actual mass of a neutron?

About 1.675 × 10⁻²⁴ g.

What is the charge of an electron?

-1 (negative)

What is the symbol for an electron?

e⁻

Where is an electron located?

In the electron cloud outside the nucleus.

What is the relative mass of an electron?

Negligible (almost 0 amu)

What is the actual mass of an electron?

9.1 × 10⁻²⁸ g.

Which two particles are found in the nucleus?

Protons and neutrons.

Which particle is found outside the nucleus?

Electron.

What is the nucleus?

The small, dense center of an atom containing protons and neutrons.

What is the electron cloud?

The region outside the nucleus where electrons are likely to be found.

What is an amu?

Atomic mass unit, a unit used to measure the mass of atoms and subatomic particles.

What makes an atom's nucleus positive?

The nucleus contains positively charged protons.

What is the overall charge of a neutral atom?

0.

When is an atom neutral?

When it has equal numbers of protons and electrons.

What determines what element an atom is?

The number of protons.

What is the atomic number?

The number of protons in an atom.

What is the mass number?

The total number of protons and neutrons.

What is the formula for mass number?

Mass number = protons + neutrons.

How do you find the number of neutrons?

Neutrons = mass number - protons.

How do you find the charge of an atom or ion?

Charge = protons - electrons.

What does it mean if two atoms have the same number of protons?

They are the same element.

What does it mean if two atoms have different numbers of protons?

They are different elements.

What are isotopes?

Atoms of the same element that have different numbers of neutrons.

What is the rule for identifying isotopes?

Same protons, different neutrons.

If two atoms have the same protons but different neutrons, what are they?

Isotopes.

If two atoms have different numbers of protons, are they isotopes?

No, they are different elements.

What is an ion?

An atom that has gained or lost electrons and therefore has a charge.

What happens when an atom loses electrons?

It becomes positively charged.

What happens when an atom gains electrons?

It becomes negatively charged.

Why does losing electrons make an atom positive?

Electrons are negative, so losing negative charges leaves more positive charge.

Why does gaining electrons make an atom negative?

The atom gains extra negative charges.

If an atom has more protons than electrons, what is its charge?

Positive.

If an atom has more electrons than protons, what is its charge?

Negative.

If an atom has 10 protons and 10 electrons, what is its charge?

0; it is neutral.

If an atom has 11 protons and 10 electrons, what is its charge?

+1.

If an atom has 10 protons and 12 electrons, what is its charge?

-2.

If an atom has 17 protons and 18 electrons, what is its charge?

-1.

If an atom has 12 protons and 10 electrons, what is its charge?

+2.

If an atom loses 2 electrons, what charge does it get?

+2.

If an atom gains 3 electrons, what charge does it get?

-3.

What did Democritus propose?

He proposed that matter was made of tiny, indivisible particles called atomos.

What does atomos mean?

Indivisible or unable to be divided.

When did Democritus live?

About 460–370 BCE.

Why wasn't Democritus's atomic theory accepted?

He did not have experimental evidence to support his idea.

What did early Greek philosophers believe matter was made of?

Air, earth, fire, and water.

Who developed the first modern atomic theory?

John Dalton.

When did Dalton develop his atomic theory?

In the early 1800s.

What was Dalton's model of the atom?

The solid ball model.

What did Dalton believe atoms were like?

Tiny solid, indivisible balls.

What was one major idea of Dalton's atomic theory?

Elements are made of extremely small particles called atoms.

What did Dalton believe about atoms of the same element?

They are similar to one another.

What did Dalton believe about atoms of different elements?

They are different from one another.

What did Dalton say happens when atoms form compounds?

Atoms combine in different ways to form compounds.

What did Dalton say happens during chemical reactions?

Atoms separate, combine, and rearrange.

What part of Dalton's theory was later proven wrong?

Atoms can be divided into smaller particles.

Who discovered the electron?

J.J. Thomson.

What experiment did J.J. Thomson use?

The cathode ray tube experiment.

What did Thomson discover?

The electron.

What charge did Thomson determine the electron had?

Negative.

What was Thomson's model called?

The Plum Pudding Model.

What did the Plum Pudding Model look like?

Negative electrons were spread throughout a positively charged substance.

Did Thomson's model have a nucleus?

No.

What is a cathode ray tube?

A sealed glass tube through which an electric current passes.

What did Robert Millikan study?

Electrons using his oil-drop experiment.

What did Millikan determine?

The charge and mass of the electron.

What is the charge of an electron according to Millikan's work?

-1.

What is the mass of an electron?

9.1 × 10⁻²⁸ g.

Who performed the Gold Foil Experiment?

Ernest Rutherford.

What did Rutherford shoot at the gold foil?

Alpha particles.

What did Rutherford expect to happen in the Gold Foil Experiment?

He expected most alpha particles to pass straight through.

Why did Rutherford expect the particles to pass through?

He thought positive charge and mass were spread evenly throughout the atom.

What actually happened in Rutherford's experiment?

Most particles passed through, some were deflected, and a very small number bounced back.

What did Rutherford conclude from most particles passing through?

The atom is mostly empty space.

What did Rutherford conclude from some particles being deflected?

There is a small, dense, positively charged nucleus.

What did Rutherford discover?

The nucleus.

What is Rutherford's model called?

The nuclear model.

Where is most of an atom's mass located?

In the nucleus.

Who discovered the proton?

Rutherford is credited with identifying the positively charged particle in the nucleus as the proton.

What is the charge of a proton?

+1.

Who discovered the neutron?

James Chadwick.

What did Chadwick discover?

The neutron.

What is the charge of a neutron?

0.

Why was the neutron important?

It helped explain the additional mass found in the nucleus.

Who developed the Bohr model?

Niels Bohr.

What did Bohr study?

The light emission spectrum of hydrogen.

What is Bohr's model called?

The planetary model or Bohr model.

What does the Bohr model show?

Electrons moving around the nucleus in specific energy levels or shells.

What happens when an electron gains energy?

It moves to a higher energy level.

What happens when an electron loses energy?

It moves to a lower energy level.