Chapter 5 Atoms and Periodic Table The Atom

Dalton’s Atomic Theory Atoms Are tiny particles of matter. of an element are similar and different from other elements. of two or more different elements combine in whole number ratios to form compounds. are separated, joined, or rearranged in a chemical reaction.

Atomic Size Smallest particle of an element that retains the properties of that element. Pure copper coin the size of a penny contains 2.4 x 1022 atoms. 1 x 108 atoms lined up next to each other would be 1cm long.

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.

Electrons JJ Thomson discovered electrons in 1897. Passed electric current through gases at low pressure sealed in tubes with electrodes at either end.

Discovery of Electron

Electrons Cathode rays attracted to metal plates with a + charge and repelled by metal plates with – charge. figured ray was made up of – charged particles. Called particles electrons (e-)

Protons Atoms are electrically neutral If atoms contain e-, must also contain + charged particles 1886 Goldstein found rays traveling in opposite direction from cathode rays (e-) Particles were protons (p+) (1840 x more mass than e-)

Neutrons In 1932, James Chadwick confirmed existence of neutrons No charge but mass almost equal to mass of p+

Particles in the Atom Question – How are subatomic particles arranged? TABLE 2.6 Question – How are subatomic particles arranged?

Rutherford’s Gold-Foil Experiment Theory at time was that – charges distributed evenly throughout + charges In Rutherford’s gold-foil experiment, positively charged particles (He atoms w/ no electrons) Were aimed at atoms of gold. Mostly went straight through the atoms. Were deflected only occasionally. 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

Rutherford’s Gold-Foil Experiment Click me!

Structure of the Atom An atom consists Of a nucleus that contains protons and neutrons. Of electrons in a large, empty space around the nucleus.

Atomic Mass Scale On the atomic mass scale for subatomic particles 1 atomic mass unit (amu) is defined as 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, 0.000549 amu.

Learning Check Identify each statement as describing a 1) proton 2) neutron 3) electron A. Found outside the nucleus. B. Has a positive charge. C. Is neutral. D. Found in the nucleus.

Solution Identify each statement as describing a 1) proton 2) neutron 3) electron A. 3 Found outside the nucleus. B. 1 Has a positive charge. C. 2 Is neutral. D. 1, 2 Found in the nucleus.

How are atoms different? It’s the number of protons!

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. 11 Na Atomic Number Symbol

Atomic Number and Protons Examples of atomic number and number of protons: 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.

Learning Check State the number of protons in each. A. A nitrogen atom 1) 5 protons 2) 7 protons 3) 14 protons B. A sulfur atom 1) 32 protons 2) 16 protons 3) 6 protons C. A barium atom 1) 137 protons 2) 81 protons 3) 56 protons

Solution State the number of protons in each. A. A nitrogen atom 2) atomic number 7; 7 protons B. A sulfur atom 2) atomic number 16; 16 protons C. A barium atom, 3) atomic number 56; 56 protons

Number of Electrons in An Atom Of an element is electrically neutral; the net charge of an atom is zero. Has an equal number of protons and electrons. number of protons = number of electrons Of aluminum has 13 protons and 13 electrons. The net charge is zero. 13 protons (13+) + 13 electrons (13 -) = 0

Mass Number The mass number Represents the number of particles in the nucleus. Is equal to the Number of protons + Number of neutrons TABLE 2.7

Atomic Models

Learning Check An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 2) 35 3) 65 B. How many neutrons are in the zinc atom? C. What is the mass number of a zinc atom that has 37 neutrons? 1) 37 2) 65 3) 67

Solution An atom of zinc has a mass number of 65. A. How many protons are in this zinc atom? 1) 30 (atomic number 30) B. How many neutrons are in the zinc atom? 2) 35 (65 – 30 = 35) C. What is the mass number of a zinc atom that has 37 neutrons? 3) 67 (30 + 37 = 67)

Learning Check An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is C. The element is 1) Si 2) Ca 3) Se

Solution An atom has 14 protons and 20 neutrons. A. It has atomic number 1) 14 B. It has a mass number of 3) 34 (14 + 20 = 34) C. The element is 1) Si (Atomic number 14)

Isotopes Isotopes 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 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

Nuclear Symbols For an atom, the nuclear symbol gives the number of Protons (p+) Neutrons (n) Electrons (e-) 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-

Learning Check Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of the following. 12C 13C 14C 6 6 6 protons ______ ______ ______ neutrons ______ ______ ______ electrons ______ ______ ______

Solution 6 6 6 protons 6 p+ 6 p+ 6 p+ neutrons 6 n 7 n 8 n 12C 13C 14C 6 6 6 protons 6 p+ 6 p+ 6 p+ neutrons 6 n 7 n 8 n electrons 6 e- 6 e- 6 e-

Learning Check A. 8 p+, 8n, 8e- ___________ Write the nuclear symbols for atoms with the following subatomic particles: A. 8 p+, 8n, 8e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________

Solution 16O A. 8p+, 8n, 8e- 8 B. 17p+, 20 n, 17e- 37Cl 17 C. 47p+, 60n, 47e- 107Ag 47

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

Solution B. 12X 14X 6 6 Both nuclear symbols represent isotopes of carbon with six protons each, but one has 6 neutrons and the other has 8. C. 15X 16X 7 8 An atom of nitrogen (7) and an atom of oxygen (8) each have 8 neutrons.

Elements and Isotopes

Isotopes of Magnesium In naturally occurring magnesium, there are three isotopes. Isotopes of Mg Atomic Mass 23.99 24.98 25.98 % abundance 78.70 10.13 11.17 24Mg 25Mg 26Mg 12 12 12

Isotopes of Sulfur A sample of naturally occurring sulfur contains several isotopes with the following abundances Isotope % abundance 32S 95.02 33S 0.75 34S 4.21 36S 0.02 32S, 33S, 34S, 36S 16 16 16 16

Atomic Mass Na 22.99 The atomic mass of an element Is 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

Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element. TABLE 2.9 32.07 amu

Atomic Mass for Cl The atomic mass of chlorine is Based on all naturally occurring Cl isotopes. Not a whole number. The weighted average of 35Cl and 37Cl.

Learning Check Using the periodic table, give the atomic mass of each element: A. calcium __________ B. aluminum __________ C. lead __________ D. barium __________ E. iron __________

Solution Using the periodic table, give the atomic mass of each element: A. calcium 40.08 amu B. aluminum 26.98 amu C. lead 207.2 amu D. barium 137.3 amu E. iron 55.85 amu

Chapter 2 Atoms and Elements 2.3 The Periodic Table Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Intro to Periodic Table

Periodic Table Dmitri Mendeleev listed elements in columns in order of increasing atomic mass He then arranged columns so that elements with most similar properties were next to each other – First Periodic table Blank spaces left bc/ no known elements with mass and properties that fit 1923 Henry Moseley determined atomic number of elements. Arranged elements in order of atomic number instead of mass – Modern table

This was my table

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

Groups and Periods Periodic Law – When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

Groups Share Similar Chemical Properties

Periodic Table

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 to the columns from left to right.

Representative Elements Several groups of representative elements are known by common names.

Alkali Metals Group 1A(1), the alkali metals, includes lithium, sodium, and potassium.

Halogens Group 7A(17), the halogens, includes chlorine, bromine, and iodine.

Learning Check Identify the element described by the following: A. Group 7A(17), Period 4 1) Br 2) Cl 3) Mn B. Group 2A(2), Period 3 1) beryllium 2) magnesium 3) boron C. Group 5A(15), Period 2 1) phosphorus 2) arsenic 3) nitrogen

Solution A. Group 7A (17), Period 4 1) Br B. Group 2A (2), Period 3 2) magnesium C. Group 5A(15), Period 2 3) nitrogen

Metals, Nonmetals, and Metalloids The heavy zigzag line separates metals and nonmetals. Metals are located to the left. Nonmetals are located to the right. Metalloids are located along the heavy zigzag line between the metals and nonmetals.

Properties of Metals, Nonmetals, and Metalloids Are shiny and ductile. Are good conductors of heat and electricity. Nonmetals Are dull, brittle, and poor conductors of heat and electricity. Are good insulators. Metalloids Are better conductors than nonmetals, but not as good as metals. Are used as semiconductors and insulators.

Comparing A Metal, Metalloid, and Nonmetal TABLE 2.5

Learning Check Identify each of the following elements as 1) metal 2) nonmetal 3) metalloid A. sodium ____ B. chlorine ____ C. silicon ____ D. iron ____ E. carbon ____

Solution Identify each of the following elements as 1) metal 2) nonmetal 3) metalloid A. sodium 1 metal B. chlorine 2 nonmetal C. silicon 3 metalloid D. iron 1 metal E. carbon 2 nonmetal

Learning Check Match the elements to the description: A. Metals in Group 4A(14) 1) Sn, Pb 2) C, Si 3) C, Si, Ge, Sn B. Nonmetals in Group 5A(15) 1) As, Sb, Bi 2) N, P 3) N, P, As, Sb C. Metalloids in Group 4A(14) 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge, Sn, Pb

Solution Match the elements to the description: A. Metals in Group 4A (14) 1) Sn, Pb B. Nonmetals in Group 5A(15) 2) N, P C. Metalloids in Group 4A(14) 2) Si, Ge