Atoms and the Periodic Table

Democritus

-tiny invisible particles

-"atomos"

John Dalton

-atoms of different elements are different masses

-combinations in specific ratios

J.J. Thomson

-negative charges

-scattered through a positively charged mass

Ernest Rutherford

-nucleus was discovered as a dense positive mass

-rest of the atom was mostly empty space

Niels Bohr

-electrons move in specific energy levels or orbits

Erwin Schrödinger

-electrons are found in space around the nucleus where they are most likely to be found

James Chadwick

-discovered neutral charges called neutrons

Dalton's atomic theory

1) Everything is made of atoms, which are the indivisible building blacks of matter and cannot be destroyed.

2) All atoms of an element are identical.

3) The atoms of different elements vary in size and mass.

4) Compounds are produced through different whole-number combinations of atoms.

5) A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.

Numbers 1 & 2 are no longer accepted because of the existence of subatomic particles and isotopes.

Atom

smallest particle of an element that is still that element

Nucleus

small positively charged center of an atom

Subatomic Particles

smaller than an atom -- protons, neutrons, electrons

Quarks

6 types that make up protons and neutrons -- grouped in pairs

Electron Cloud

the area around the nucleus of an atom where elecrons are most likely to be found

Atomic mass unit

amu

Atomic Number

number of protons in an atom

Isotopes

atoms of the same element with different numbers of neutrons

Average atomic mass

the weighted average mass of all the naturally occurring isotopes of an element

Mass Number

protons + neutrons

Writing Isotopes

ex) Carbon - 12

Chart

Who created the periodic table?

Dmitri Mendeleev

What did Mendeleev arrange the elements by?

atomic mass

What does periodic mean?

repeating

What did Mendeleev do to his periodic table when certain elements didn't fit in the right columns?

left empty spaces for unknown elements

Who fixed the periodic table?

Henry Moseley

What did Moseley do to change the periodic table?

rearranged the table based on increasing atomic number

Define Periodic Table

arrangement of elements by increasing atomic number and periodic changes in physical and chemical properties

What is a period on the periodic table?

horizontal rows of elements on the periodic table

How are periods numbered?

1-7

What do periods represent?

the number of electron shells in an element

What is a group on the periodic table?

vertical columns of elements on the periodic table

How are groups numbered?

1-18

What do groups represent?

the number of valence electrons in an element

What are energy levels?

areas where electrons are found around the nucleus

When an electron is closer to the nucleus, it has ______ energy. When an electron is farther from the nucleus, it has ______ energy.

lower; higher

Where is a valence electron?

outer energy level

What is the maximum number of electrons that can go into each energy level?

Level 1 = 2

Level 2 = 8

Level 3 = 18

Level 4 = 32

What is maximum number of electrons that can be in the valence electron shell of an atom?

8 (exception, level 1 holds 2)