Using the Periodic Table

6Carbon

C12.011 amu

• Atomic number- always a whole number, increases in order, represents the number of protons in each atom

• Atomic name, often in Latin, sometimes uses a common name, sometimes there are disagreements

• Atomic symbol – often, but not always, matches the name; Always capitalize the first (only the first ) letter

• Atomic mass- the mass of the atoms based on the average of all the most common isotopes

Atoms

Chapter 6

• Aristotle, the famous Greek philosopher and scientist, argued that a substance could be divided again and again, forever getting smaller and smaller pieces

• During his time people believed the universe was made of four elements; fire, water, earth and air.

• The idea of “uncuttable” particles was first suggested by Democritus around 440 B.C.

• “Atomos” means indivisible

Section 1 Atomic Theory

• Atomic Theory (by John Dalton) published in 1803– All substances are made

from atoms. Atoms cannot be created, divided or destroyed.

– Atoms of the same element are exactly alike.

– Atoms can join together to form new substances.

• JJ Thomson discovered the negatively charged electrons inside the atom.

• Ernest Rutherford discovered that the atom is mostly empty space with a tiny positive nucleus and orbiting electrons.

• Neils Bohr determined that electrons traveled along paths or energy levels.

• Schrodinger & Heisenberg

Pictures of Atoms

Atomic Size• Atoms are extremely small…• Aluminum foil is 100,000 atoms thick.

• A Penny has 20,000,000,000,000,000,000,000 atoms!

What’s Inside an Atom?Protons (+):

Positively Charged Particles

Mass=1amu

Location: Nucleus

Neutrons (0):

Particles with No Charge

Mass=1amu

Location: Nucleus

Electrons (-):

Negatively Charged Particles

Mass= almost zero

Location: Electron Clouds

Parts of the Atom

Particle Charge Location Size

Proton Positive In the nucleus 1 a.m.u.

Neutron No charge (neutral)

In the nucleusAlmost 1 a.m.u.

Electron NegativeOutside the nucleus, orbiting at nearly the

speed of light

Very tiny, 1/1000th a.m.u.

Structure of the Atom

• Protons– Positively charged– Found in the nucleus of the

atom (center)– Mass of 1 amu (atomic mass

unit)– Gives the element its atomic

number on the periodic table• #1 (hydrogen) has 1 proton

• #4 (beryllium) has 4 protons

+

Protrons were discovered by Ernest Rutherford in 1911 and he discovered the empty space within an atom in 1909

• Neutrons– Neutral charge ( no

charge)– Found in the nucleus

(center) – Mass slightly smaller

than a proton, still considered 1 amu

– Protons + Neutrons atomic mass (rounded to the nearest whole number)

N

• Isotope– Atoms can often be found

with different numbers of neutrons

• Some atoms have only one stable isotope, others have several

• Averaging the masses of the isotopes in their correct percentages gives the exact atomic mass for each element

• Unstable isotopes break down (radioactive decay)

Hydrogen (H-1), most common 99.9%

tritium (H-3), least common, radioactive

deuterium (H-2),

• Electrons– Negatively charged

particles– Found outside the nucleus,

moving at nearly the speed of light, in specific levels

– Most commonly atoms are neutral particles having equal numbers of protons and electrons

– Very small ( about 1/1000th of a proton)

Proton

Neutron

Electron

Electrons were discovered by J.J. Thompson in 1897

* In 1913 Niels Bohr suggested that electrons travel in specific paths called Electron Shells

• Each level can only contain a certain number of electrons before it is full

• Each level will fill completely before electrons go to the next level

• Lower levels fill first

1832