Rutherford’s Atom/PastElectrons orbit nucleus similar as planets to the sun

Atom of the PresentElectrons orbit nucleus in the form of clouds

• Proton = + charge• Neutron = neutral charge• Electron = - charge

• Protons (positive) are bigger than electrons. The part of an atom that gives an element its identity.

• Neutrons (neutral) are slightly bigger in mass than a proton.

• Electrons (negative) charge, have a mass of close to zero-negligible

Atomic Mass Units (amu): roughly equal to the mass of a proton or neutron.**the mass of an atom is measured in amu’s

1 amu= 1/12 (mass of 12/6C atom) = 1.66x10^-24g

Particle location Charge(C) Mass (g)Mass (amu)

ProtonInside nucleus

1.602 X 10-191.673X10-24

1.0073=1

NeutronInside nucleus

01.675X10-24

1.0087=1

ElectronOutside nucleus

-1.602 x10-147.109X10-28

0.0006=0

Atomic numbers• Atoms of each element contain a unique positive

charge in their nucleus.

• Discovery helped solve the mystery of what makes the atoms of one element difference from those of another.

• Atoms identity comes from number of protons in nucleus.

• Number of protons in an atom is called atomic number.

• Every element has a unique atomic number.

• Elements atomic number is just above the chemical symbol on periodic table.

• Individual atom is electrically neutral-means number of protons always equal number of electrons.

Electron Number

• An Element’s atomic number also indicates number of electrons in its atoms.

• Atom can lose or gain its electrons, giving an overall positive or negative charge.

Ions• Ions are atoms that have lost or gained one or more electrons giving them a positive or negative charge!

For example: Na (Sodium), has originally 11 electrons but when an electron is lost it becomes a postive ion. Na +

If an ion looses an election it has a positive charge.

If an ion gains an electron it has a negative charge.

What causes an atom to become an ion?• When an atom loses or gains one or more

electrons it acquires a net electrical charge called an ion.

• The net charge of an ion is found by subtracting the number of electrons from the number of protons

Charge of Ion = number of protons – number of electrons

A neutral magnesium atom (atomic number=12) has 12 protons/electrons. If it loses 2 electrons it becomes an ion with a charge of 2+.

Number of protons 12Number of electrons - 10 Charge of Ion 2+

19. Cu²+

20. F-

29

9

Ion Protons Electrons

27

10

Isotopes• Isotopes are atoms that have the same

number of protons but different numbers of neutrons

• Most elements in the first two rows of the periodic table have at least 2 isotopes with one being more common than the other

• In nature, elements are almost always found as a mixture of isotopes

Hmm

Hydrogen Deuterium Tritium

•For example, the most common isotope of hydrogen has no neutrons at all

•There's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons.

Neutron

Proton

Isotopes of Hydrogen

Most common isotope

Differences between isotopes?

• Isotopes react in the same way as others of the same element

• The major difference between two isotopes is their mass – Isotopes with more neutrons have a higher mass than those with fewer neutrons

• “Heavy” and “light” are often used to describe an isotope

• To identify an isotope more specifically, chemists add a number after the elements name.

ex. Carbon-11 Carbon-12 Carbon-14• This number is called the isotope’s mass number

and is the sum of the isotope’s number of protons and neutrons.

• For example, an atom with 17 protons and 20 neutrons has a mass number of 37.

Atomic mass

Atomic Number/number of protons

Atomic mass: weighted average of the masses of the existing isotopes of an element.

Q. What is the name of the Nitrogen isotope with 7 protons and 12 neutrons?

A. Nitrogen-19

iodine-128

potassium-41

53

19

53

19

75

21

Atom Protons Neutrons Electrons

Examples

Mass Number – the sum of an isotope’s protons and neutrons.

To name an isotope using chemical symbols, simply place the atom’s mass number to the upper left of the element symbol. For example 37Cl.

#neutrons = atomic mass – atomic number

37 – 17 = 20 neutrons

How many protons, neutrons, and electrons are present?5626

STEP 1: The atomic number in the lower left corner = 26 protons. The difference between the mass number and the atomic number is 56 – 26 = 30. There are 30 neutrons.

STEP 2: The charge on the ion, 2+ shows us that there are 2 more protons than electrons, indicating that there are 24 electrons.

Fe 2+

Isotope Symbols

141

56

Mass number (M)

Atomic number (Z)

ChargeBa2+

Number of protons = ZNumber of neutrons = M – Zcharge = Z– Number of electrons