The Atom Chapter 3

From Idea to Theory Democritus, Greek philosopher, 400 B.C., introduced the concept of an atom, an ‘indivisible’ particle. Democritus, Greek philosopher, 400 B.C., introduced the concept of an atom, an ‘indivisible’ particle.

Basic Laws of Matter Law of Conservation of Mass- mass can’t be created or destroyed during ordinary chemical rxns and physical changes. Law of Conservation of Mass- mass can’t be created or destroyed during ordinary chemical rxns and physical changes. Carbon + oxygen  carbon dioxide Carbon + oxygen  carbon dioxide 12 g 32 g 44 g 12 g 32 g 44 g

Law of Definite Proportions- a certain cmpd will always have the same proportion of each element, by mass and by atoms. Law of Definite Proportions- a certain cmpd will always have the same proportion of each element, by mass and by atoms. Ex. Carbon dioxide always has one carbon atom to 2 oxygen atoms OR 12 g carbon and 32g oxygen Ex. Carbon dioxide always has one carbon atom to 2 oxygen atoms OR 12 g carbon and 32g oxygen

Basic Laws of Matter Law of Multiple Proportions- more than one cmpd can be formed from the elements by having a different whole number ratio of the atoms Law of Multiple Proportions- more than one cmpd can be formed from the elements by having a different whole number ratio of the atoms Ex. CO, CO 2 Ex. CO, CO 2

Dalton’s Atomic Theory 1. All matter is composed of small particles called atoms. 2. Atoms of the same element are the same physically and chemically.

3. Atoms can’t be divided, created, or destroyed. 4. Atoms of different elements combine in whole- number ratios to form cmpds. 5. In chemical rxns, atoms are combined, separated, or rearranged. Section Review p69

Structure of Atom Atom- smallest particle of an element that retains the chemical properties of that element. Atom- smallest particle of an element that retains the chemical properties of that element.

Subatomic particles: Subatomic particles: Nucleus- center of atom Nucleus- center of atom Proton- Positively charged particle in nucleus Proton- Positively charged particle in nucleus Neutron- neutral particle in nucleus, a tiny bit larger than proton Neutron- neutral particle in nucleus, a tiny bit larger than proton Electron- negatively charged particle, about 2000X smaller in mass that proton Electron- negatively charged particle, about 2000X smaller in mass that proton

Cathode Ray Tube Cathode Ray tube experiment by JJ Thomson discovered the electron (See pg. 70) Cathode Ray tube experiment by JJ Thomson discovered the electron (See pg. 70)

Conclusions from Experiment: Conclusions from Experiment: 1. Rays cast shadow on other end of tube- light 2. Rays push paddle along- some form of matter 3. Rays deflected by magnet- not light 4. Rays deflected by negative charge- therefore cathode rays are made up of negatively charged particles called electrons.

Discovery of Nucleus Robert Millikan determine the mass of an electron to be X kg. Since atoms are neutral, atoms must have positive charge. Robert Millikan determine the mass of an electron to be X kg. Since atoms are neutral, atoms must have positive charge. Ernest Rutherford’s Gold Foil Experiment discovered the nucleus. See pg. 73 Ernest Rutherford’s Gold Foil Experiment discovered the nucleus. See pg. 73

Gold Foil Experiment Conclusion of Gold Foil Experiment Conclusion of Gold Foil Experiment 1. Most of the alpha particles passed through – atom mostly empty space. 2. Few deflected and reflected alpha particles - small, dense, positive, nucleus in atom Note: nuclear forces hold neutrons together in the nucleus. Section Review p74

Counting Atoms Atomic number- number of protons in nucleus of an atom. Number of protons in the nucleus determines which element it is. Atomic number- number of protons in nucleus of an atom. Number of protons in the nucleus determines which element it is. Ex. All C atoms have 6 protons. No other element has 6 protons. Locate the atomic number of carbon on the periodic table Ex. All C atoms have 6 protons. No other element has 6 protons. Locate the atomic number of carbon on the periodic table

Isotopes Isotopes- atoms of the same element with different number of neutrons, so their masses are different. Isotopes of the same element are chemically different Isotopes- atoms of the same element with different number of neutrons, so their masses are different. Isotopes of the same element are chemically different

Ex. 3 forms of hydrogen Ex. 3 forms of hydrogen 1. Protium- one proton, no neutrons – % in nature 2. Deuterium- one proton, one neutron – 0.015% in nature 3. Tritium- one proton, two neutron – radioactive- very little in nature, can be made

Counting Atoms Mass number- number of protons and neutrons in the nucleus of an isotope Mass number- number of protons and neutrons in the nucleus of an isotope Ex. Ex. Protium’s mass number is 1 (1p + 0n), hydrogen-1 (hyphen notation), nuclear symbol = Protium’s mass number is 1 (1p + 0n), hydrogen-1 (hyphen notation), nuclear symbol = Deuterium’s mass number is 2 (1p + 1n), hydrogen-2, nuclear symbol = Tritium’s mass number is 3 (1p +2n), hydrogen-3, nuclear symbol =

Practice 1. How many protons, electrons, and neutrons are in chlorine-37? Practice p78

Atomic Mass Mass of one atom of carbon-12 is 12 amu (atomic mass unit). So all atomic masses use C- 12 as standard. Mass of one atom of carbon-12 is 12 amu (atomic mass unit). So all atomic masses use C- 12 as standard. Average atomic mass of an element is the weighted average of all the naturally occurring isotopes of that element Average atomic mass of an element is the weighted average of all the naturally occurring isotopes of that element The average atomic mass depends on the mass and abundance of each element’s isotope. The average atomic mass depends on the mass and abundance of each element’s isotope.

Atomic Mass Calculations 1. Calculate the average atomic mass of copper given the following abundances and atomic masses for each isotope. Isotope 1: amu and 69.17% Isotope 2: amu and 30.83%

What is the mass of one aluminum atom? One gold atom? One neon atom? What is the mass of one aluminum atom? One gold atom? One neon atom?

Mass to Number of Atoms 1 mole = 6.02 X particles = Avogadro’s number 1 mole = 6.02 X particles = Avogadro’s number Molar Mass = number of grams of one mole of a substance Molar Mass = number of grams of one mole of a substance Practice: What is the molar mass of each element? He, Li, Hg Practice: What is the molar mass of each element? He, Li, Hg

Mass and Moles 1. What is the mass in grams of 3.50 moles of copper? 2. How many moles of aluminum are in 11.9 g? Practice p83

Moles to Atoms 3. How many moles of silver are 3.01 X atoms of silver? 4. How many atoms of tungsten make up 1.34 X moles?

Atoms to Mass 5. What is the mass in grams of 7.5 X atoms of nickel? 6. How many atoms of sulfur, S, are in 4.00 g of sulfur? 7. What is the mass of 3.10 X atoms of Cl?