Exam 3 – Unit 2 Complete individually. No notes. No talking. No sharing calculators. When finished submit up front. Begin reading Chapter 3 pages 67-76 and Chapter 1 pages 16-20 Complete Part 1 of Unit Packet

Exam 3 Analysis Average Measurement and Calculations #1: +____/25 % Phases and KMT #2 +____/15 % (up from %) Matter and Changes #3 +____/10

Unit 3 – Atoms: The Building Blocks of Matter Learning Objectives and Practice Packet

Periodic Table Terminology 1. Periods: Horizontal row of elements in the periodic table. 2. Group (family): A vertical column of elements in the periodic table. (Have the same number of valence electrons)

Atomic Theory Continues… We have come so far in our understanding of atoms. Centuries of researching and countless scientists devoting their lives to create the understanding of the atom today (textbook concepts). However it is NOT over. The more we understand about atoms (how they work, their make up, etc…) the greater our ability to advance science and technology in all aspects of our lives (i.e. medicine).

Check for Understanding What is the charge of a proton? Where would you find a proton in an atom? What is the charge of an electron? Where would you find an electron in an atom? What is the charge of a neutron? Where would you find a neutron in an atom? How big is an electron compared to a proton? How big is a neutron compared to a proton?

Atoms: The Building Blocks of Matter Basic Laws (1790s) Law of Conservation of Mass Mass is neither created nor destroyed during chemical reactions or physical changes. Law of Definite Proportions A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or source of the compound. Law of Multiple Proportions If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combine with a certain mass of the first element is ALWAYS a ratio of small WHOLE numbers.

Atomic Theory - Video John Dalton (1808) English Schoolteacher Proposed an explanation of the 3 basic laws (as mentioned previously) Dalton’s Atomic Theory (5 Statements) All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole number ratios to form compounds. In chemical reactions, atoms are combined, separated, or rearranged.

Modern Atomic Theory Dalton’s Theory has been modified to fit new findings. (Science is NOT static) Example: Today we know that atoms are divisible into even smaller particles 1. Subatomic Particles (protons, neutrons, and electrons) 2. Protons and Neutrons are made up of quarks Important concepts All matter is composed of atoms Atoms of any one element differ in properties from atoms of another element remain unchanged.

The Atom The smallest particle of an element that retains the chemical properties of that element. Consists of two regions: Nucleus 1. Small region located at the center of an atom 2. Made up of at least one positively charged particle (proton) 3. Made up of usually one or more neutral particles (neutrons) Region surrounding the nucleus – Electron Cloud 1. Very large compared to size of nucleus 2. Contains the negatively charged particles (electrons)

Electron Discovery JJ Thomson (1897) Cathode-ray tubes 1. Electric current was passed through various gases at low pressures. 2. The glow was caused by a stream of particles – cathode ray 3. The ray was deflected by a magnetic field and away from a negatively charged object. Concluded that all cathode rays are composed of identical negatively charged particles (electrons) Plum pudding model 1. Negative electrons spread throughout the positive charge of the rest of the atoms. 2. Plums= electrons ; pudding=positive charge

Electron Discovery Cont… Robert Millikan (1909) Measured the charge of the electron. (Charge to mass ratio) Mass of electron = 9.109 x 10-31kg Or about 1/2000 the mass of a hydrogen atom Inferences from findings… Because atoms are electrically neutral, they must contain a positive charge to balance the negative electrons. Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass.

Nuclear Atom Ernest Rutherford (1911) Bombarded a thin piece of gold foil with fast-moving alpha particles (positively charged particles) Concluded that deflected alpha particles must have experienced some powerful force within the atom The source of this force must occupy a very small amount of space Force must be caused by a very densely packed bundle of matter with a positive electric charge (Nucleus) Volume of nucleus was very small compared with the total volume of an atom. If the nucleus were the size of a pea, then the size of the atom would be about the size of a football field.

Refresh: What are Atoms? Atoms are tiny particles that determine properties of all matter. Atoms are the building blocks for molecules. Atoms form elements. Element: A substance that cannot be broken down into simpler substances by chemical means.

Parts of an Atom Proton: A subatomic particle that has a positive charge and is found in the nucleus of the atom. Neutron: A subatomic particle that has NO charge and is found in the nucleus of the atom. Electron: A subatomic particle that has a negative charge and moves around the outside of the nucleus.

Label the Atom

Subatomic Particles Particle Charge Mass (kg) Location Proton +1 1.67 x 10-27 nucleus Neutron Electron -1 9.11 x 10-31 Outside nucleus

Electron Orbital -Electrons orbit the nucleus in orbital clouds. -Electrons with different amounts of energy exist in different energy levels.

The Electron Cloud Model

Electrons in each energy level Each energy level can hold a limited number of electrons. The lowest energy level is the smallest and the closest to the nucleus.

Atomic Number The atomic number of an element is the number of protons in the nucleus of an atom of that element.

Formative Assessment Read pages 77-87 and complete Part 2 of the unit packet! Bring Questions!!

Formative Assessment Review and Questions

Atomic Number The atomic number of an element is the number of protons in the nucleus of an atom of that element.

Charge of Atoms Atoms are not charged even though they have particles that contain charges. Atoms are neutral because they have EQUAL numbers of protons and electrons. Ex: Helium Atom Charge of 2 protons: Charge of 2 neutrons: Charge of 2 electrons: Total charge of He atom: +2 -2

Mass Number The sum of the protons and neutrons in the nucleus is the mass number of that particular atom. (mass # = p + n)

Atomic Number vs. Mass Number Atomic Number: Equal to the number of protons in the nucleus of the atom. (number of electrons = the number of protons) Mass Number: Equal to the number of protons AND neutrons in an atom’s nucleus. Average Atomic Weight (below symbol on PT): Weighted average of the atomic masses of the naturally occurring isotopes of an element We will round this number to the nearest hundredth (TWO decimal places) Example Oxygen’s average atomic mass is 15.9994 = 16.00

Application Iodine (I) Iron (Fe) Atomic number ____ Atomic Number ____ Atomic Mass ____ Atomic Mass ____   Number of Protons ____ Number of Protons ____ Number of Neutrons ____ Number of Neutrons____ Number of electrons ____ Number of Electrons ____

Application Nickel (Ni) Radon (Rn) Atomic number ____ Atomic Number ____ Atomic Mass ____ Atomic Mass ____   Number of Protons ____ Number of Protons ____ Number of Neutrons ____ Number of Neutrons____ Number of electrons ____ Number of Electrons ____

Isotopes Isotopes of an element have different mass numbers because they have different numbers of neutrons, but they all have the same atomic number.

Isotope Examples Carbon – 12 6 protons 6 electrons 6 neutrons

Li Lithium Example 6,7 3 Mass Numbers Symbol Atomic Number Element Name

One More Example Ag Silver 47 107

Isotope Tables Breaking it down… To find the symbol – determine the atomic number of the element. This is the number of protons To find the protons- determine the atomic number of the element. To find the electrons – equal to the number of protons of a neutral atom To find neutrons: Mass Number – Atomic Number = Number of Neutrons To find Mass Number: Atomic Number + Number of Neutrons = Mass Number

Isotopes

Practice

For Tomorrow… Complete Isotope Worksheet and Part 3 worksheet!