Chem 2A Ch. 3 Atoms and the Periodic Table

f-Block element

An inner transition metal element that results from the filling of f orbitals.

Neutron

A electrically neutral sub-atomic particle.

Problem 3.10 Complete the fallowing isotope symbols: a.11/5? b. 56/?Fe

A. The elemental symbol is 11/5 B B. The atomic number is 56/26 Fe

Halogen

An element found in group 17 of the periodic table

Work example 3.2 Phosphorous has atomic number of Z = 15. How many protons, electrons, and neutrons are there in phosphorous atoms, which have a mass number of A = 31?

It has 15 protons, 15 electron, and 16 neutrons. Z = 15 A = 31 31-25 = 16 neutrons

Shell (electron)

A grouping of electrons in an atom according to energy.

Nucleus

The dense, central core of an atom that contains protons and neutrons.

Problem 3.18 How many electrons are present in an atomin ehich the 1s, 2s, and 2 p subshells are filled? Name the element.

1s^2 2s^2 2p^6 Z = 10 Neon has 10 atoms

Problem 3.19 How many electrons are present in an atom in which the first and second shell and the 3 subshell are filled? Name the element.

1s^2 2s^2 2p^6 3s^2 or [Ne] = 3s^2 Z = 12 The element is Magnesium.

Work Example How many electrons are present in an atom that has its first and second shells filled and has 4 electrons in its third shell? Name the element.

2 + 8 + 4 = 14 electrons which means the element is silicon (Si).

Work example 3.3 An atom contains 28 protons and has an A = 60. Give the number of electrons and neutrons in the atom, and identify the element.

28 protons, 28 electrons, and 32 neutrons. Z = 28 A = 60 60-28 = 32 neutrons The element with Z = 28 and 32 neutrons is Nickel

Problem 3.6 The Uranium used in nuclear reactors has Z = 92 and A = 235. How many protons, neutrons, and electrons are in these uranium atoms?

92 protons, 92 electrons, and 143 neutrons Z = 92 A = 235 235 A - 92 Z = 143 neutrons

Subshell (electron)

A grouping of electrons in a shell according to the shape of the region of space they occupy.

s-Block element

A main group element that results from the filling of an s orbital.

p-Block element

A main group element that results from the filling of p-orbitals.

Electron

A negatively charged sub-atomic particle.

Proton

A positively charged sub-atomic particle.

Atomic Theory

A set of assumptions proposed by the English scientist John Dalton to explain the chemical behavior of matter.

d-Block element

A transition metal that results in the filling of d orbitals.

Problem 3.11 Locate aluminum in the periodic table, and give its group number and period number.

Aluminum is in Group 3A, and period 3

Valence electron

An electron in the outermost, or valence, shell of an atom.

Noble Gas

An element in Group 18 of the periodic table. These elements are nonreactive.

Alkali metal

An element in group 1A of the periodic table.

inner transition metals

An element in one of the 14 groups shown separately at the bottom of the periodic table,

Main Group Elements

An element in one of the two groups on the left or six groups on the right of the periodic table.

Alkaline Earth Metals

An element in the group 2A of the periodic table.

Problem 3.7 A certain atom has A = 52 and contains 28 neutrons. Identify the element.

Chromium Cr 52 A - 28 atoms = 24 atomic mass

Work Example 3.10 Using n to represent the number of the outer shell, write a general outer-shell configuration for the elements in group 6A.

For group 6A, the general outer-shell configuration is ns^2 np^4.

Work example 3.4 Gallium is a metal with a very low melting point-it will melt in the palm of your hand. It has two naturally occurring isotopes: 60.4 % is Ga-69 (mass = 68.9257 amu), and 39.6% is Ga-71 (mass = 70.9248 amu). Calculate the average atomic weight for gallium.

Ga-69 (mass = 68.9257 amu) Ga-71 (mass = 70.9248 amu) Average atomic weight of gallium (amu) = ? Atomic weight = sum (isotopic abundance) X (isotopic mass) Atomic weight = (0.604) (68.9257 amu) = 41.6311 amu + (0.396) (70.9248 amu) = 28.0862 amu Atomic weight = 69.7 amu 3 sig. figs.

Key Concept Problem 3.27 identify the group number, and write the general outer-shell configuration for the elements indicated in red in the following periodic table.

Group 6A, ns^2 np^4

Problem 3.8 Potassium (K) has two naturally occurring isotopes: K-39 (93.1 %; mass = 38.9637 amu), and K-41 (6.88%; 40.9618 amu). Calculate the atomic weight for potassium. How does your answer compare with the atomic mass given in the list inside the front cover of this book?

K-39 (mass = 38.9637 amu) K-41 (mass = 40.9618 amu) Average atomic weight of gallium (amu) = ? Atomic Weight = (0.931)(38.9637 amu) = 36.2752 amu + (0.0688)(40.9618 amu) = 2.8181 amu Atomic Weight = 39.1 amu 3 sig. figs. They match up in the book

Group

One of the 18 vertical columns of elements in the periodic table.

Period

One of the 7 horizontal rows of elements in the periodic table.

Problem 3.13 There are five elements in group 5A of the periodic table. Identify them, and give the period of each.

The 5 elements in group 5A are N, P, As, Sb, and Bi

Key Concept problem 3.23 Identify the atom with the fallowing orbital-filling diagram. 1s^2 2s^2 2p^6 3s^2 3p^6

The atom with 18 electrons is Argon (Ar)

Problem 3.9 Chlorine, an element present in common table salt (sodium chloride), has two naturally occurring isotopes, with mass numbers 35 and 37. Write the symbols for both, including their atomic numbers and mass numbers.

The atomic number for Chlorine is 17, so 35/17 Cl and 37/17 Cl are the answers.

Problem 3.12 Identify the group 1B element in period 5 and the group 2A element in period 4.

The element in 1B and period 5 is Ag and theelement in 2A and period 4 is Ca.

Problem 3.21 Write electron configuration for the elements with atomic numbers 14 and 36.

The element with the atomic number 14 (Si) has the electron configuration of: 1s^2 2s^2 2p^6 3s^2 3p^2 The element with the atomic number 36 (Kr) has the electron configuration of: 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^3

Valence shell

The outermost electron shell of an atom.

Atom

The smallest and simplest particle of an element

Electron Configuration

The specific arrangement of electrons in an atom's shells and subshells.

Subatomic Particles

Three kinds of fundamental particles from which atoms are made: protons, neutrons, and electrons.

Work Example 3.11 How many electrons are in a tin atom? Give the number of electrons in each shell. How many valence electrons are there in a tin atom? Write the outer-shell configuration for tin.

Tin has the atomic number of 50 and is in group 4A. The number of electrons in each shell is: Shell #: 1, 2, 3, 4, 5 # of electron: 2, 8, 18, 18, 4

Problem 3.4 What pattern do you see in your answers to problem 3.3?

When the mass in grams is numerically equal to the mass in amu, there are 6.02 X 10^23 atoms.

Atomic mass vs. molar mass

While atomic mass and molar mass are numerically equivalent, keep in mind that they are vastly different in terms of scale, as represented by the vast difference in the magnitudes of their respective units (amu versus g).

Work Example Show how the electron configuration of magnesium can be assigned.

Z = 12 Magnesium has the configuration of 1s^2 2s^2 2p^6 3s^2 or [Ne] 3s^2

Transition Metal Element

an element in one of the 10 smaller groups near the middle of the periodic table.

Isotopes

atoms with identical atomic numbers but different mass numbers

Work example 3.1 How many atoms are their in a small piece of aluminum foil with a mass of 0.100 g? The mass of an atom of aluminum is 27.0 amu.

mass of aluminum foil = 0.100 g 1 Al atom = 27.0 amu Number of Al atoms = ? 1 amu = 1.660 539 X 10^-24 g ---> (1 amu/1.660 539 X 10^-24 g) (0.100g)(1 amu/1.660 539 X 10^-24 g)(1 Al atom/ 27.0 amu) = 2.23 X 10^23 Al atom

Problem 3.1 What is the mass in amu of a nitrogen atom weighing 2.33 X 10^-23 g?

nitrogen atom = 2.33 X 10^-23 g 1 amu = 1.660 539 X 10^-24 g 2.33 X 10^-23 g ( 1 amu/ 1.660 539 X 10^-24 g) = 14.0 amu

Problem 3.2 What is the mass in grams of 100,000 gold atoms, each weighing 197 amu?

100,000 gold atoms 197 amu 100,000 gold atoms = 1.97 x 10^7 amu 1.97 x 10^7amu (1 amu / 1.660 539 X 10^-24 g) = 3.27 x 10^-17grams

Problem 3.25 Identify the group number, give the number of electrons in each occupied shell, and write its outer-shell configuration.

Group 2A

Problem 3.26 for chlorine, identify the group number, give the number of electrons in each occupied shell, and write its outer-shell configuration.

Group 7A, 1s^2 2s^2 2p^6 3s^2 3p^5

Problem 3.22 for an atom containing 33 electrons. identify the incompletely filled subshell, and show the paired and/or unpaired electrons in this subshell using up and down arrows.

The atom containing 33 electrons is As (arsenic): 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10

Work Example 3.5 Identify element X in the symbol 194/74X, and give its atomic number, mass number, number of protons, number of electrons,and number of neutrons.

Z = 74 A = 194 Platinum has the isotope 194/74Pt. 74 protons, electrons, and 116 neutrons. 194 - 74 = 116 neutrons.

Key Concept Problem 3.16 identify the element shown in red on the fallowing periodic table, tell its group number, its period number, and whether it is a metal, nonmetal, or metalloid.

Zinc is the element and it is a Metal.

Work Example 3.8 Write the electron configuration of phosphorus, Z = 15, using arrows to show how electrons in each orbital are paired.

[P] 1s^2 2s^2 2p^6 3s^2 3p^3

Problem 3.15 Locate (a) Krypton, (b) Strontium, (c) nitrogen, and (d) cobalt in the periodic table. Indicate which category applies to each; (i) metal, (ii) nonmetal, (iii) transition element, (iv) main group element, (v) noble gas.

a. Krypton is a Noble Gas b. Strontium is a Metal c. Nitrogen is a Nonmetal d. Cobalt is a Metal

Atomic mass unit (amu)

a convenient unit for describing the mass of an atom; 1 amu = 1/12 the mass of a carbon-12 atom

Orbital

a region of space within an atom where an electron in a given subshell can be found

Problem 3.3 How many atoms are in each of the following? a. 1.0 g of hydrogen atoms, each mass of 1.0 amu. b. 12.0 g of carbon atoms, each a mass of 12.0 amu. c. 23.0 g of sodium atoms, each a mass of 23.0 amu.

a. (1.0 g)(1 amu / 1.660 539 X 10^-24 g)(1 H2 atoms / 1 amu) = 6.02 X 10^23 H2 atoms b. (12.0 g)(1 amu / 1.660 539 X 10^-24 g)(1 C atom/ 12.0 amu) = 6.02 X 10^23 C atoms c. (23.0 g)(1 amu/1.660 539 X 10^-24 g)(1 Na atom/ 23.0 amu) = 6.02 X 10^23 Na atoms

Problem 3.17 What is the maximum number of electrons that can occupy the following subshells. a. 3p subshell b. 2s subshell c. 2p subshell

a. 6 electrons b. 2 electrons c. 6 electrons

Problem 3.20 Write electron configuration for the fallowing elements. a. C b. Na c. Cl d. Ca

a. C Z = 6 1s^2 2s^2 2p^2 b. Na Z = 11 1s^2 2s^2 2p^6 3s^1 c. Cl Z = 17 1s^2 2s^2 2p^6 3s^2 3p^5 d. Ca Z = 20 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2

Problem 3.24 Write the electron configuration for the following elements, using both the complete and the shorthand notations.Indicate which electrons are the valence electrons. a. F b. Al c. As

a. F Z = 9 1s^2 2s^2 2p^5 or 2s^2 2p^5 b. Al Z = 13 1s^2 2s^2 2p^6 3s^2 3p^1 or 3s^2 3p^1 c. As Z = 33 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^2 or 4s^2 3d^10 4p^2

Work Example 3.9 Write the electron configuration for the following elements, using both the complete and the shorthand notations. Indicate which electrons are the valence electrons. a. Na b. Cl c.Zr

a. Na row 3 and column 1 Na: 1s^2 2s^2 2p^6 3s^1 or [Ne] 3s^1 b. Cl is in row 3 and column 5 Cl: 1s^2 2s^2 2p^6 3s^2 3p^5 or [Ne] 3s^2 3p^5 c. Zr is in row 5 and column 2 Zr: 1s^2 2s^2 2p^6 3s^1 3p^6 4s^2 5s^2 4d^2 or [Kr] 5s^2 4d^2

Problem 3.5 use the list inside the front cover to identify elements with the fallowing atomic numbers: Z = 75 Z = 20 Z = 52

a. Re (Rhenium) b. Ca (Calcium) c. Te (Tellurium)

Problem 3.14 Identify the fallowing elements as metals, nonmetals, or metalloids: a. Ti b. Te c. Se d. Sc e. At f. Ar

a. Ti is a metal b. Te is a metalloid c. Se is a Nonmetal d. Sc is a metal e. At is a metalloid f. Ar is a noble gas