The Atom

Chapter 4 Sect 1

0.0000000000000000000000016726g0.0000000000000000000000016748g0.0000000000000000000000000009109g

V. Parts of the Atom: A. Nucleus – the solid dense core of the atom that contains the protons and neutrons1. Proton- what can you find out about them?

A. positively charged particleB. mass = 1 amu (atomic mass unit)C. The number of protons identifies the

elementD. Number of protons = the atomic

numberE. Quark – 3 small particles that make up

a proton

Parts of the Atom: 2. Neutron – what can you find out about them?

A. particles with no chargeB. mass = 1 amu (same as proton)C. # of protons + # of neutrons = atomic

massD. Adding or taking away neutrons DOES

NOT change the atom, it makes different isotopes

E. Quark – 3 quarks make up a neutron

Parts of the Atom: B. Electron cloud – surrounds the nucleus and contains electrons1. Electrons – what can you find out about them?

A. Negatively charged particleB. Mass very small amu = 0C. It takes 1800 electrons to equal the

mass of 1 protonD. # of electrons = # of protons in a

neutral atom

VI. Atomic Number – what is it and why is it important?

The atomic number is the number of protons in the nucleus of the atom.

It is important because the atomic number identifies the element.

Table #1

Proton number Atomic number Element Symbol

8 8 Oxygen O

1 1 Hydrogen H

6 6 Carbon C

7 7 Nitrogen N

10 10 Neon Ne

13 13 Aluminum Al

VII. Sub atomic Particles

Subatomic particle Atomic mass in atomic mass units

charge location

Proton 1 amu +

positive

nucleus

Neutron 1 amu 0

neutral

nucleus

Electron 0 amu _

negative

Orbits around nucleus in electron

cloud

VIII. What is mass number and why is it important?

The mass number is the number of protons plus the number of neutrons in the nucleus.

The mass number is important because you can calculate the number of neutrons to identify isotopes

Mass number – Atomic Number = Neutrons

Recall**The only thing you need to know to identify an element is the number of protons.**Each protons weighs 1 amu and each neutron weighs 1 amu.**When you add up the number of protons and the number of neutrons you get the mass number.

Why don’t you add in the number of electrons?

Electrons are too small to calculate into the equation Remember! Electrons are 1/1800 of a proton or neutron

So, if your atomic number is 11 – what element are you? Atomic Number 11 = Sodium (Na)

X. Isotopes Most elements have naturally occurring

isotopes. What is an Isotope? Atoms with the same number of protons but

different numbers of neutrons are isotopes. If you gain a neutron, you will be heavier (more

massive) Why? You are adding a neutron which has a mass

of 1 amu If you lose a neutron, you are lighter (less

massive) Why? You are taking away 1 amu

Isotopes or different elements?

D and F are different elements different # of protons

J and L are isotopes same # of protons, different # of neutrons

X and Y are different elements different # of protons

Q and R are isotopes same # of protons, different # of neutrons

Isotopes or different elements?

T has 20 protons and 20 neutronsZ has 20 protons and 21 neutronsT and Z are isotopes

same # of protons, different # of neutrons

A has 31 protons and 39 neutronsE has 32 protons and 38 neutronsA and E are different elements

different # of protons

The atomic mass that you see on the Periodic Table is the average of all the isotopes of that element. How does this explain why there are no whole atomic mass numbers on the Periodic Table?

There are no whole number masses on the Periodic Table because averages usually don’t equal a whole number.

How to read a Periodic Table

C12.011

6

Atomic Number

Atomic Symbol

Atomic Mass

How to read a Periodic Table

Li6.941

3

Atomic Number

Atomic Symbol

Atomic Mass

How to read a Periodic Table

O15.999

8

Atomic Number

Atomic Symbol

Atomic Mass

Middle of page 5

Before we move on, let’s review protons and neutrons. Where are they located? In the nucleus. They each have a mass of 1 amu. An electron is much smaller than a proton or a neutron and has a mass of 0 amu. Electrons are located in the electron cloud of the atom. Protons have what charge? Positive (+) Electrons have what charge? Negative (-)

Table 3 (Use inside back cover)

Element Atomic number

Proton number

Atomic mass

(rounded)

Neutrons Electrons Charge of atom

C

Carbon 6 6 12 6 60

Neutral

Na

Sodium 11 11 23 12 110

neutral

Si

Silicon 14 14 28 14 140

neutral

O

Oxygen 8 8 16 8 80

neutral

3 Main Parts

Protons with 1 atomic mass unit or amu and a + charge

Neutrons with 1 atomic mass unit or amu and a 0 charge

Electrons with 0 atomic mass unit or amu and a - charge

Unlike protons and neutrons in an atom, the electrons are arranged in a particular order. The electrons fill the energy shells closest to the nucleus first and then fill outward:

The first energy shell can hold up to 2 electrons The second energy shell can hold up to 8

electrons The third energy shell can hold up to 18

electrons The fourth energy shell can hold up to 32

electrons

Electron Shell Diagram – Phosphorous

First Energy Level

Second EnergyLevel

Third EnergyLevel

Electron Shell Diagram –Phosphorous

First Energy Level

Second EnergyLevel

Third EnergyLevel

XI. Forces that hold the atom together 1. Gravity - even in an atom… depends on:

A. How big (massive) the objects are B. how far apart they are

2. Electromagnetic forces…like charges do what? Unlike charges do what? A. Like charges repel B. Unlike (opposite) charges attract C. Electrons repel electrons, but attract protons D. Protons repel protons, but attract electrons3. Strong force (nuclear force) – holds protons together in the

nucleus

4. Weak force – plays a role in radioactive (unstable) atoms when a neutron changes into a proton and an electron

IV. History of the Atom

A. Democritus (400 BC) 1. Said elements are invisible particles called

atoms 2. The atoms were “indivisible” or “uncutable”

B. Aristotle (384 – 322 BC) 1. Disagreed with Democritus 2. All matter was made up of the 4 elements:

Air, Earth, Water, and Fire

History of the Atom (cont.)

C. John Dalton (late 1700’s) 1. Atoms cannot be created, divided or

destroyed. 2. Atoms of the same element are alike. 3. Atoms join with other atoms to make new

substances D. J.J. Thompson (1897)

1. Found that atoms are made of smaller parts. 2. Discovered a negative charge – later called

the electron.

History of the atom (cont.)

E. Ernest Rutherford (1909) 1. Proved atoms are not solid 2. They are mostly empty space, but with a

solid nucleus

F. Neils Bohr (1913) 1. Suggested that electrons traveled around the

nucleus in definite paths (Sun and planets model for atoms)

2. Electron can jump between levels.