Chapter 4 Atoms and Elements Elements and Symbols The Periodic Table The Atom Atomic and Mass Numbers Isotopes and Atomic Mass Electron Energy Levels You will need your textbook or copy of a periodic table for class !!!!!!!!!!

Pure Substances Elements Compounds

Elements Elements are Pure substances that cannot be separated into simpler substances by ordinary laboratory processes. The building blocks of matter. gold carbon aluminum Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Sources of Some Element Names Some elements are named for planets, mythological figures, minerals, colors, scientists, and places.

Historical Perspective

Symbols of Elements A symbol Represents the name of an element. Consists of 1 or 2 letters. Starts with a capital letter. Examples: 1-Letter Symbols 2-Letter Symbols C carbon Co cobalt N nitrogen Ca calcium F fluorine Al aluminum O oxygen Mg magnesium

Symbols from Latin Names Several symbols are derived from Latin names as shown below: Cu, copper (cuprum) Au, gold (aurum) Fe, iron (ferrum) Ag, silver (argentum)

Pure Substances A pure substance is classified as An element when composed of one type of atom. A compound when composed of two or more different elements combined in a definite ratio.

Elements v. Compounds v. Mixtures: Review Recall definition of compound. A compound is when two or more different elements combine in a definite ratio. NaCl MgCl2 AlCl3 Molecular element is when both of the atoms in the molecule are the same element. H2 N2 O2 F2 Cl2 Br2 I2

A closer look at the Periodic Table

Modern Periodic Table Mendeleev – Father of the Periodic Table Periodic Law of the Elements – when elements are arranged in a particular order (increasing atomic number), elements of similar properties occur at periodic intervals Arranged into: Groups/families – vertical columns Periods – horizontal rows http://www.woodrow.org/teachers/chemistry/institutes/1992/MENDELEEV.GIF

Arrangement of the Periodic Table The blocks of the periodic table:

The Periodic Table – All Stretched Out

Groups and Periods On the periodic table Elements are arranged according to similar properties. Groups contain elements with similar properties in vertical columns. Periods are horizontal rows of elements.

Groups and Periods (Rows) Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Group Numbers Group Numbers Use the letter A for the representative elements 1A to 8A and the letter B for the transition elements. Also use numbers 1-18 for the columns from left to right.

Names of Some Representative Elements Several groups of representative elements are known by common names. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Alkali Metals Group 1A(1), the alkali metals, includes lithium, sodium, and potassium. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Halogens Group 7A(17) the halogens, includes chlorine, bromine, and iodine. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check Identify the element described by the following: 1. Group 7A (17), Period 4 A) B) C) 2. Group 2A(2), Period 3 A) B) C) 3. Group 5A(15), Period 2 A) B) C)

Special Element: C Carbon is a very special element. Specialized industrial uses. elemental forms organic molecules such as solvents, fuels, pharmaceuticals, etc. Central element in biomolecules found in living systems.

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Learning Check Match the elements to the description: 1. Metals in Group 4A(14) A) B) C) 2. Nonmetals in Group 5A(15) A) B) C) 3. Metalloids in Group 4A(14) A) B) C)

A closer look still

The Conjecture of Atoms As early as 500 B.C., Greek Philosophers proposed that all matter is made up of atoms Atom: The smallest individual particle of an element that maintains the properties of that element Atomos - indivisible http://members.aol.com/dcaronejr/ezmed/atom.jpg http://www.aperfectworld.org/clipart/science_technology/atom.gif

Dalton’s Law of Atomic Theory All matter is composed of extremely small particles called atoms. Atoms of a given element are identical in their physical and chemical properties, while atoms of different elements differ in their physical and chemical properties. http://www.kjemi.uio.no/software/dalton/graphics/john_dalton.gif

Dalton’s Law of Atomic Theory 3. Atoms of different elements combine in simple, whole-number ratios to form compounds. 4. In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. http://www.kjemi.uio.no/software/dalton/graphics/john_dalton.gif

Subatomic Particles Today, we know that atoms are made up of smaller, more fundamental particles called subatomic particles. Protons, Electrons & Neutrons

Subatomic Particles Atoms contains subatomic particles Protons have a positive (+) charge. Electrons have a negative (-) charge. Like charges repel and unlike charges attract. Neutrons are neutral. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Rutherford’s Gold-Foil Experiment In Rutherford’s gold-foil experiment Positively charged particles were aimed at atoms of gold. Most went straight through the atoms. Only a few were deflected. Conclusion: There must be a small, dense, positively charged nucleus in the atom that deflects positive particles that come close.

Rutherford’s Gold-Foil Experiment Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Structure of the Atom An atom consists Of a nucleus that contains protons and neutrons. Of electrons in the large empty space around the nucleus. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Atomic Mass Scale On the atomic mass scale for subatomic particles 1 atomic mass unit (amu) is equal to 1/12 of the mass of the carbon-12 atom. A proton has a mass of about 1 (1.007) amu. A neutron has a mass of about 1 (1.008) amu. An electron has a very small mass (0.00055 amu).

Particles in the Atom Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Atomic Number 11 Na Atomic Number Symbol The atomic number Is specific for each element. Is the same for all atoms of an element. Is equal to the number of protons in an atom. Appears above the symbol of an element in most periodic tables. 11 Na Atomic Number Symbol

Atomic Numbers and Protons Examples: Hydrogen has atomic number 1, every H atom has one proton. Carbon has atomic number 6, every C atom has six protons. Copper has atomic number 29, every Cu atom has 29 protons. Gold has atomic number 79, every Au atom has 79 protons.

Atomic Models Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Learning Check State the number of protons in each. 1. A ________ atom A) protons B) protons C) protons 2. A ________ atom A) protons B) protons C) protons 3. A ________ atom A) protons B) protons C) protons 4. A ________ atom A) protons B) protons C) protons

Electrons in An Atom An atom of any element is electrically neutral; the net charge of an atom is zero. In an atom, the number of protons is equal to the number of electrons. number of protons = number of electrons For example, an atom of aluminum has 13 protons and 13 electrons. The net charge is zero. 13 protons (13 +) + 13 electrons (13 -) = 0 What if there are more electrons than protons? or more protons than electrons?

Mass Number The mass number Represents the number of particles in the nucleus. Is equal to the Number of protons + Number of neutrons

Learning Check An atom has 14 protons and 20 neutrons. 1. Its atomic number is A) B) C) 2. Its mass number is A) B) C 3. The element is A) B) C)

Learning Check An atom of zinc has an atomic number of 30, and mass number of 65. 1. How many protons are in this zinc atom? A) B) C) 2. How many neutrons are in the zinc atom? 3. What is the mass number of a zinc atom that has 37 neutrons?

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Isotopes and Atomic Mass Are atoms of the same element that have different mass numbers. Have the same number of protons, but different numbers of neutrons.

Nuclear Symbol A nuclear symbol (aka atomic symbol) Represents a particular atom of an element. Gives the mass number in the upper left corner and the atomic number in the lower left corner. Example: An atom of sodium with atomic number 11 and a mass number 23 has the following atomic symbol: mass number 23 Na atomic number 11

Information from Nuclear Symbols The nuclear symbol indicates the number of protons (p+), neutrons, (n), and electrons (e-) in a particular atom. 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15 e- 30 e-

Nuclear / Atomic Symbols Charge = Number of protons - number of electrons Mass number = number of protons + number of neutrons A Q X Z Atomic number = number of protons Defines the element

Nuclear / Atomic Symbols Charge = number of protons – number of electrons Mass number = number of protons + number of neutrons A Q X Z Atomic number = number of protons

Nuclear / Atomic Symbols Charge = number of protons – number of electrons Mass number = number of protons + number of neutrons A Q X Z Atomic number = number of protons

Nuclear / Atomic Symbol Notation vs. The Periodic Table Notation 20 Ca 40.078 40 2+ Ca 20

Learning Check 1. Which of the following pairs are isotopes of the _________________? 2. In which of the following pairs do both atoms have _________________? A. 15X 15X 8 7 B. 12X 14X 6 6 C. 15X 16X 7 8

Atomic Mass Na 22.99 The atomic mass of an element Is usually listed below the symbol of each element on the periodic table. Gives the mass of an “average” atom of each element compared to 12C. Is not the same as the mass number. Na 22.99

Calculating Average Atomic Mass The calculation for the average atomic mass requires the Percent (%) abundance of each isotope. Atomic mass in amu of each isotope of that element. Sum of the weighted averages. mass isotope(1) x (%) + mass isotope(2) x (%) + … 100 100

Consider the element Magnesium Chapter 4, Unnumbered Figure, Page 111 Atomic symbol for an isotope of magnesium 58

Chapter 4, Unnumbered Figure, Page 112 The nuclei of three naturally occurring magnesium isotopes have different numbers of neutrons. 59

Atomic Mass of Magnesium The atomic mass of Mg Is due to all the Mg isotopes. Is a weighted average. Is not a whole number. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Calculating Atomic Mass Isotope Mass Abundance 24Mg = 23.985 amu x 78.70/100 = 18.88 amu 25Mg = 24.986 amu x 10.13/100 = 2.531 amu 26Mg = 25.983 amu x 11.17/100 = 2.902 amu Atomic mass (average mass) Mg = 24.31 amu Mg 24.31

Atomic Mass for Cl The atomic mass of chlorine is the weighted average of two isotopes 35Cl and 37Cl. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Calculating Atomic Mass for Cl 35Cl has atomic mass 34.97 (75.76%) and 37Cl has atomic mass 36.97 (24.24%). The atomic mass and percent of each isotope are used to calculate the contribution of each isotope to the weighted average. 34.97 x 75.76 = 26.49 amu 100 36.97 x 24.24 = + 8.962 amu 100 35.45 amu The sum is the weighted average or atomic mass of Cl. 35.45 amu

Learning Check Gallium is an element found in lasers used in compact disc players. In a sample of gallium, there is 60.11% of 69Ga (atomic mass 68.93) atoms and 39.89% of 71Ga (atomic mass 70.93) atoms. What is the atomic mass of gallium? →

Solution 69Ga 68.93 amu x 60.11 = 41.43 amu (from 69Ga) 100 71Ga Atomic mass Ga = 69.72 amu 31 Ga 69.72

Examples of Isotopes and Their Atomic Masses Table 4.8 Most elements have two or more isotopes that contribute to the atomic mass of that element. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings