Objectives Identify three subatomic particles Understand how subatomic

Objectives Identify three subatomic particles Understand how subatomic particle was discovered Compare the properties of the subatomic particles Distinguish between atomic number and mass number Calculate the number of protons, electrons and neutrons in an atom

Subatomic Particles Subatomic particles - 3 important to chemistry: protons, neutrons, electrons

Protons Part of the nucleus Have positive (+) charge

Protons Definition - a positively charge subatomic particle that is found in the nucleus of an atom About Protons - proton is nearly 2000 times more massive than the electron, but equal in charge and opposite in sign to the electron - number of protons in the nucleus is electrically balanced by an equal number of electrons ex. oxygen atom: contains 8 electrons and protons: neutral atom, no net charge

Electrons Orbit around the nucleus Have negative (-) charge

Electron Definition - a negatively charged subatomic particle that is found in the space outside the nucleus - name comes from the Greek word for amber - Amber: material discovered by early Greeks that was found to exhibit the effects of electrical charging ex. Ben Franklin: Key/Kite - lead others to experiment with electric currents through gases in sealed tubes

Neutrons Part of the nucleus Have neutral charge

Neutrons Definition - is a neutral subatomic particle that is found in the nucleus of the atom - mass almost exactly equal to that of the proton

Comparing Subatomic Particles

Atomic Number Definition - number of protons in the atom ex. Oxygen 8 p + 8 n = 16 - elements are classified by this number - continues up to 119 - unique to a given element - all atoms are electrically neutral, meaning the number of electrons must equal the number of protons - this arrangement of elements by their atomic numbers makes up the periodic table - Usually located at the upper left hand corner

Atomic Number Atoms are composed of identical protons, neutrons, and electrons How then are atoms of one element different from another element? Elements are different because they contain different numbers of PROTONS The “atomic number” of an element is the number of protons in the nucleus # protons in an atom = # electrons

Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. Element # of protons Atomic # (Z) Carbon 6 6 Phosphorus 15 15 Gold 79 79

Complete Symbols Contain the symbol of the element, the mass number and the atomic number. Mass Superscript → number Subscript → Atomic number X

Symbols n Find each of these: a) number of protons b) number of neutrons c) number of electrons d) Atomic number e) Mass Number 80 35 Br

Symbols n If an element has an atomic number of 34 and a mass number of 78, what is the: a) number of protons b) number of neutrons c) number of electrons d) complete symbol

Symbols n If an element has 91 protons and 140 neutrons what is the a) Atomic number b) Mass number c) number of electrons d) complete symbol

Symbols n If an element has 78 electrons and 117 neutrons what is the a) Atomic number b) Mass number c) number of protons d) complete symbol

Mass Number - although a given type of atom will usually contain a certain number of neutrons in the nucleus, a small percentage will not ex. most hydrogen atoms contain no neutrons - a small percentage contain one neutron and a smaller percentage two neutrons What do we call atoms with a different number of neutrons? - isotopes

Mass Number Definition - the total number of protons and neutrons in the nucleus of an atom Tells us how much one atom weighs in atomic mass units. -mass number – atomic number = neutrons ex. N: mass number of 14 atomic number of 7 7 neutrons

How to Calculate the Mass Number Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n 0

Mass Number Cont. - usually found at the bottom of the atomic symbol, and sometimes found written at the bottom left of an atomic symbol ex. 16 O

Atomic Mass

Atomic Mass Definition - mass of an atom in atomic mass units (amu) - atoms have very little mass - equal to 1/12 th of the mass of carbon - often an average mass - weighted mass AMU or the Dalton (Da) - equal to 1. 6605402 x 10 -27 kg

Atomic Mass How heavy is an atom of oxygen? It depends, because there are different kinds of oxygen atoms. We are more concerned with the average atomic mass. This is based on the abundance (percentage) of each variety of that element in nature. We don’t use grams for this mass because the numbers would be too small.

Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Symbol Carbon-12 12 C Carbon-13 13 C Carbon-14 14 C Composition of the nucleus 6 protons 6 neutrons 6 protons 7 neutrons 6 protons 8 neutrons Carbon = 12. 011 % in nature 98. 89% 1. 11% <0. 01%

Isotopes Frederick Soddy (1877 -1956) proposed the idea of isotopes in 1912 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.

Isotopes Atoms with the same number of protons but different numbers on neutrons Example: Carbon So you can change the number of neutrons and the element still maintains its identity

Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Isotope Hydrogen– 1 (protium) Hydrogen-2 (deuterium) Hydrogen-3 (tritium) Proton Electrons Neutrons s 1 1 0 1 1 1 2 Nucleus

Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons.

Mass Number/Avg Atomic Weight

Objectives Describe Bohr’s model of the atom and the evidence for energy levels Explain how the electron cloud model represents the behavior and locations of electrons in atoms

Bohr’s Model of the Atom Bohr’s Model - an early conceptual model of the atom - classic planetary model in which electrons whirl around the small but dense nucleus: like planets orbiting the Sun - developed by the Danish physicist Niels Bohr in 1911 - each electron has a certain energy that is determined by it’s path around the nucleus - explains how atoms (lose) emit or (gain) absorb energy resulting energy: energy level

Bohr’s Model: Energy Levels Definition - any of the possible energies an electron may have in an atom Evidence - measured amount of energy gained or lost - when energy is lost we often see it as a light ex. fireworks - 1925 this model no longer explained all observations being made by scientists and new models were created ex. Electron cloud model

Atoms have neutral charge # of Protons (+) = # of Electrons (-) = 0 charge Example: Hydrogen How many electrons does C have?

Electrons orbit in “shells” 1 st shell can fit 2 electrons 1 st period/row 2 nd and 3 rd shells can fit 8 electrons 2 nd period/row 3 rd period/row

Atoms want their shells to be full 2 electrons in first shell 8 electrons in 2 nd and 3 rd shells Examples:

DRAWING BOHR MODELS

Bohr Models 1. Bohr models are used to predict reactivity in elements. 2. Reactivity refers to how likely an element is to form a compound with another element. 3. When looking at Bohr models, we look at its valence electrons (the electrons on the last energy level) to determine reactivity.

Drawing Bohr Models 1. Draw the nucleus. 2. Write the number of neutrons and the number of protons in the nucleus. 3. Draw the first energy level. 4. Draw the electrons in the energy levels according to the rules below. Make sure you draw the electrons in pairs. 5. Keep track of how many electrons are put in each level and the number of electrons left to use.

Rules for Energy Levels 1. Level 1 (closest to the nucleus) can hold a maximum of 2 e. 2. Level 2 can hold a max of 8 e. 3. Level 3 can hold a max of 18 e. 4. Level 4 can hold a max of 32 e. You must fill one level before going on to draw the next level!

Guided Practice In order to draw Bohr models of these elements, you must first determine the number of protons, neutrons, and electrons. Once you have found this information, follow the directions to draw your model. 6 C Carbon 12. 011 6 6 6 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 2 How many valence (outer) electrons does this element have? ____ 4 Bohr Model:

Guided Practice 16 S Sulfur 32. 066 16 16 16 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 3 How many valence (outer) electrons does this element have? ____ 6 Bohr Model:

Guided Practice 3 Li Lithium 6. 941 3 4 3 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 2 How many valence (outer) electrons does this element have? ____ 1 Bohr Model:

Guided Practice 10 Ne Neon 20. 180 10 10 10 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 2 How many valence (outer) electrons does this element have? ____ 8 Bohr Model:

Guided Practice 15 P Phosphorus 30. 974 15 16 15 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 3 How many valence (outer) electrons does this element have? ____ Bohr Model: 5

Guided Practice 11 Na Sodium 22. 990 11 12 11 Protons: _____ Neutrons: _____ Electrons: ______ How many energy shells will this have? ____ 3 How many valence (outer) electrons does this element have? ____ Bohr Model: 1