I. From Philosophical Idea to Scientific Theory (p. 66-71) Ch. 3 – The Atom I. From Philosophical Idea to Scientific Theory (p. 66-71) Foundations Dalton’s Theory Modern Theory C. Johannesson

A. Foundations Law of Conservation of Mass In a chemical reaction, matter is neither created or destroyed In the 1790’s a new emphasis was placed on the quantitative study of matter in chemical reactions. Aided by improved balances, investigators began to accurately measure the masses of elements and compounds they were studying. This led to the discovery of 3 basic laws… C. Johannesson

A. Foundations Law of Definite Proportions A chemical compound contains the same elements in the same proportions regardless of the size of the sample C. Johannesson

A. Foundations Law of Multiple Proportions the ratio of elements that makes up a compound is always a whole # ratio C. Johannesson

B. Dalton’s Atomic Theory All matter is composed of atoms The atoms of any one element (Na) are all alike, but differ from the atoms of other elements (C) Atoms cannot be divided, created, or destroyed The atoms of elements combine in whole # ratios to form compounds Atoms are combined, separated, or rearranged in a chemical reaction C. Johannesson

C. Modern Atomic Theory Correction to Dalton’s Theory… Atoms are composed of even smaller particles called protons, neutrons, and electrons C. Johannesson

II. Atomic Structure (p. 72-76) Ch. 3 – The Atom II. Atomic Structure (p. 72-76) Subatomic Particles Thomson’s Cathode Ray Rutherford’s Experiment Composition C. Johannesson

A. Subatomic Particles equal in a neutral atom Atomic Number NUCLEUS ELECTRONS equal in a neutral atom PROTONS NEUTRONS NEGATIVE CHARGE QUARKS Atomic Number equals the # of... POSITIVE CHARGE NEUTRAL CHARGE Most of the atom’s mass. C. Johannesson

A. Subatomic Particles Quarks component of protons & neutrons 6 types He 3 quarks = 1 proton or 1 neutron C. Johannesson

B. Thomson’s Cathode Ray Experiment Play “Cathode Ray Tube” by dchummer 2:49 on YouTube Famous experiment that led to the discovery of the Electron

B. Thomson’s Cathode Ray Experiment Thomson concluded that the particles in the beam had a negative charge and a very small mass

C. Rutherford’s Gold Foil Experiment If an atom were the size of a large football stadium, the nucleus would be about the size of a marble….the atom is mostly empty space.

D. Composition of the Atomic Nucleus The atom’s nucleus are made of two kinds of particles- protons and neutrons Protons have a (+) charge equal in magnitude to the (-) charge of an electron Neutrons are neutral; they contain no charge Atoms are neutral because they contain equal #’s of protons and electrons

D. Composition of the Atomic Nucleus The atom’s nucleus takes up most of the atom’s mass while electrons take up most of it’s volume. Nuclear Forces allow protons and neutrons to be closely packed together without repelling one another Generally, like-particles repel each other, yet there is a strong attraction between the protons in the nucleus.

D. Composition of the Atomic Nucleus Did You Know? Unleashed nuclear forces provide the energy associated with nuclear power or the detonation of an atomic weapon.

Ch. 3 – The Atom II. Masses of Atoms (p. 75-80) Mass Number Isotopes Relative Atomic Mass Average Atomic Mass C. Johannesson

A. Atomic Number An element’s Atomic Number is the # of protons in its nucleus and is used to identify that element. The Periodic Table organizes elements in order of increasing atomic #’s from 1-118. Hydrogen’s (H) atomic # = 1 Helium’s (He) atomic # = 2 Lithium’s (Li) atomic # = 3 Etc… The IDENTITY of the atom is determined by the # protons. The # of electron/neutrons can vary and the atom will still be of the same element. But if the # of protons changes, then the atom becomes an atom of a different element. C. Johannesson

A. Mass Number mass # = protons + neutrons always a whole number © Addison-Wesley Publishing Company, Inc. always a whole number NOT on the Periodic Table! C. Johannesson

B. Isotopes   C. Johannesson

B. Isotopes There are 3 types of Hydrogen (H) atoms, each with a diff. # of neutrons We call these “isotopes” of Hydrogen C. Johannesson

B. Isotopes 1) Nuclear symbol: Mass # Atomic # Isotopes are atoms of the same element with different #’s of neutrons and therefore different mass numbers. 2 methods for specifying: 1) Nuclear symbol: Mass # - The atoms of many naturally occurring elements have different #’s neutrons. Atomic # 2) Hyphen notation: carbon-12 C. Johannesson

B. Isotopes # neutrons = mass # - atomic # C. Johannesson © Addison-Wesley Publishing Company, Inc. The # of neutrons is found by subtracting the atomic # from the mass # C. Johannesson

B. Isotopes How many protons, electrons, and neutrons are there in an atom of Chlorine-37? C. Johannesson

B. Isotopes Chlorine-37 atomic #: mass #: # of protons: # of electrons: # of neutrons: 17 37 20 C. Johannesson

B. Isotopes How many protons, electrons, and neutrons are there in an atom of Bromine-80? -35 protons, 35 electrons, 45 neutrons C. Johannesson

What is the nuclear symbol for Carbon-12, Carbon-13, & Carbon-14? B. Isotopes What is the nuclear symbol for Carbon-12, Carbon-13, & Carbon-14? C. Johannesson

B. Isotopes Write the hyphen notation for the isotope with 15 electrons and 15 neutrons Phosphorus-30 C. Johannesson

C. Relative Atomic Mass Relative Atomic Mass: mass of a particular isotope of an element. Ex- naturally occurring Copper (Cu) consists of 69.15% Copper-63; atomic mass = 62.93 amu 30.85% Copper-65; atomic mass = 64.93 amu - Most elements occur naturally as mixtures of isotopes. - The % of each iso. Is nearly always the same no matter where the element is found. - This % is taken into account when calculating the element’s avg. atomic mass. C. Johannesson

D. Average Atomic Mass Average Atomic Mass: weighted average of all isotopes on the Periodic Table round to 2 decimal places - Most elements occur naturally as mixtures of isotopes. - The % of each iso. Is nearly always the same no matter where the element is found. - This % is taken into account when calculating the element’s avg. atomic mass. C. Johannesson

D. Average Atomic Mass or Avg. Atomic Mass Avg. Atomic Mass - Most elements occur naturally as mixtures of isotopes. - The % of each iso. Is nearly always the same no matter where the element is found. - This % is taken into account when calculating the element’s avg. atomic mass. Avg. Atomic Mass = (mass)(decimal) + (mass)(decimal) C. Johannesson

D. Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass 16.00 amu C. Johannesson

D. Average Atomic Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass 35.40 amu C. Johannesson

Practice Problems… C. Johannesson

According to the Law of Conservation of Mass, what mass would compound AB have, if the atomic mass of A = 2 mass units and that of B = 3 mass units? 5 C. Johannesson

What two regions make up an atom? Nucleus, Electrons C. Johannesson

What are the two kinds of particles that make up the nucleus of an atom? Protons, Neutrons C. Johannesson

It is equal to the # protons In a neutral atom, how do you determine the # of electrons? It is equal to the # protons C. Johannesson

Where is the majority of an atom’s mass located? The Nucleus C. Johannesson

Where is the majority of an atom’s volume located? Electrons C. Johannesson

Total # of protons + neutrons What is the mass # of an isotope? Total # of protons + neutrons C. Johannesson

Write the hyphen notation for an isotope who’s atomic # = 2 and mass # = 4? Helium-4 C. Johannesson

Write the hyphen notation for an isotope who’s atomic # = 19 and mass # = 39? Potassium-39 C. Johannesson

Protons = 11, Electrons = 11, Neutrons = 12 How many protons, electrons, and neutrons are there in an atom of sodium-23? Protons = 11, Electrons = 11, Neutrons = 12 C. Johannesson

Protons = 20, Electrons = 20, Neutrons = 20 How many protons, electrons, and neutrons are there in an atom of calcium-40? Protons = 20, Electrons = 20, Neutrons = 20 C. Johannesson

Protons = 29, Electrons = 29, Neutrons = 35   Protons = 29, Electrons = 29, Neutrons = 35 C. Johannesson

Protons = 47, Electrons = 47, Neutrons = 61   Protons = 47, Electrons = 47, Neutrons = 61 C. Johannesson

Silicon-28 Write the Nuclear Symbol and Hyphen Notation for: - an isotope with a mass # = 28 and an atomic # = 14   Silicon-28 C. Johannesson

Iron-56 Write the Nuclear Symbol and Hyphen Notation for: - an isotope with 26 protons and 30 neutrons   Iron-56 C. Johannesson