Basic Atomic StructureDemocritus

Dalton

Subatomic Particles

Symbol Notation

Isotopes

Average Atomic Mass

Democritus (460-370BC)Before Democritus… Classification system: earth, wind, fire, water

Named parts of matter “atomos.”(translation: not able to be cut)How did he come up with this?

Later scientists realized that the atom consists of charged particles.

John Dalton’s Atomic Theory of Matter

All elements are composed of tiny indivisible particles called atoms

Atoms of the same element are identical, atoms of different elements are different and have different properties.

Atoms of different elements can mix in whole number ratios to form compounds

Chemical reactions cause atoms to separate, but not change into different atoms

Which hold true?

Law of Constant Composition (Proust): In a given compound the relative numbers and kinds of atoms are constant. (postulate #3)

Law of Conservation: matter can neither be created nor destroyed (postulate #4)

NEW** Law of Multiple Proportions: If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole #’s.

Water Vs. Hydrogen Peroxide8.0g of O combines with 1.0g of H to form water16g of O combines with 1.0g of H to form hydrogen peroxideWhat can you conclude about the ratios of hydrogen and oxygen in these two compounds?

Subatomic Particles

Three Kinds of Sub-Atomic ParticlesProtons: +1.602x10-19C chargeNeutrons: NO chargeElectrons: -1.602x10-19C chargeAtoms have an equal # of protons and electrons so they have no NET electrical charge.For convenience, the charges are expressed as multiples rather than in coulombs. Protons have a +1 charge while electrons have a -1 charge.

Charge Mass (amu)

Location Discoverer

proton

1+ 1 nucleus ThomsonGoldstein

neutron 0 1 nucleus Chadwick

electron 1-

1/1840 outside

nucleusThomson

Comparing Subatomic Particles

The proton gives identity to an atom, the electron gives personality.

Ernest Rutherford:http://www.learnerstv.com/animation/animation.php?ani=121&cat=Chemistry

Conclusion: the nucleus is small and highy positive.Most of the atom is empty space.

Mass Number & Atomic Number

Mass Number = Number of protons + neutrons

Atomic Number = Number of protons

Complete the Table

Symbol Atomic Number

Mass Number

Number of p+

Number of n0

Number of e-

9 10

Na 15

47 25

55 25

S2- 32

Ga3+ 39

Isotopes Have the Same…

Number of protons

Atomic Number

Number of electrons

Isotopes Have Different…

Number of neutrons

Mass Number

Mass

n0

Isotopes of Hydrogen

Hydrogen-1 Hydrogen-2 Hydrogen-3

Protium Deuterium Tritium

The mass of an atom is EXTREMELY small!The heaviest known atom is 4x10-22g.For convenience, (thank you)... we express the size of atoms in a derived unit, the a.m.u.(Atomic Mass Unit)Diameters of atoms fall between 1x10-10m and 5x10-10m, or 100-500pm, or 1-5Angstroms1A=10-

10m (both pm and A are commonly used)

How many atoms are in one penny?24,000,000,000,000,000,000,000 or 2.4 x 1022

How many people live on this planet?6,000,000,000 or 6 x 10 9

Atomic Mass Unit (amu)

carbon-12 isotope used as standard 1 atom of carbon-12 = 12 amu carbon-12 has 12 particles with mass mass of proton = 1 amu mass of neutron = 1 amu 12

C 6

Average Atomic Mass

Weighted average of all isotopes

Seen as mass number on periodic table

Units in amu

To Calculate Average Atomic Mass You Need…

Number of Isotopes

Mass of Isotopes

Percent Relative Abundance

Calculating Average Atomic Mass

Mass x Rel. Abundance

Mass x Rel. Abundance

Average Atomic Mass

Isotope A

Isotope B

AVERAGE ATOMIC MASSCALCULATING AVERAGE ATOMIC MASSAtomic Mass or Atomic Weight: a calculated percentage of existing isotopes according to abundance: mass isotope x % abundance (DECIMAL FORM) mass isotope x % abundance+ mass isotope x % abundance

Find the Number of Neutrons:a) Oxygen-17 d)Bromine-80b) 32S e) 207 Pbc) 108Ag f) 25 Mg 47

12

Write the symbols for each element with the correct atomic number and mass number in proper notationa) O-16, O-17, O-18b) Cr-50, Cr-52, Cr-53

Element X has two natural isotopes...X-10 and X-11X-10 weighs 10.012amu and is 19.91% abundantX-11 weighs 11.009amu and is 80.09% abundantWhat is the atomic mass?

Naturally occurring chlorine is 75.78% 35Cl, which has an atomic mass of 34.969amu, and 24.22% 37Cl, which has an atomic mass of 36.966amu. Calculate the average atomic mass of chlorine.

Three isotopes of silicon occur in nature: 28Si (92.23%), which has a mass of 27.97693amu; 29Si(4.68%), which has a mass of 28.97649amu; and 30Si(3.09%), which has a mass of 29.97377amu. Calculate the atomic weight of silicon.

Boron has two isotopes, B-10 and B-11...Which is more abundant?

Silicon has 3 isotopes, Si-28,29,30Which is more abundant?