Unit 04 Test Review

Isotope

Atoms of the same element with different numbers of neutrons.

Radioactivity

The process in which some substances spontaneously emit radiation.

3. Identify the atom containing the following number of electrons. -34 -5 -31 -61 -94

-34 electrons: Selenium -5 electrons: Boron -31 electrons: Gallium -61 electrons: Promethium -94 electrons: plutonium

4. Identify the atom containing the following number of protons. -74 -20 -49 -70 -93

-74 protons: Tungsten -20 Protons: Calcium -49 protons: Indium -70 protons: Ytterbium -93 protons: Neptunium

Vocabulary Unit 4

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alpha particle

A particle with two protons and two neutrons, with a 2+ charge; is equivalent to a helium-4 nucleus, can be represented by a; and is emitted during radioactive decay.

Nuclear Radiation

A reaction that involves a change in the nucleus of an atom.

Radioactive decay

A spontaneous process in which unstable nuclei lose energy by emitting radiation.

Proton

A subatomic particle in an atom's nucleus that has a positive charge of 1+.

5. Atoms of which element contain 18 protons and 18 electrons?

Argon

6. The other three naturally occurring isotopes of chromium have mass numbers of 50, 52, and 54. Describe how atoms of these isotopes differ from the isotope mentioned in example problem 4-1.

Chromium-50 has 26 neutrons, Chromium-52 has 28 neutrons, and Chromium-54 has 30 neutrons.

Why was the discovery of the electron considered evidence for the existence of positively charged particles in the atom?

J.J Thomson's experiments with the cathode ray tubes showed that all atoms contain tiny negatively charged particles called 'electrons'. Since electrons have a negative charge and there are atoms with no charge, there must be positive charges present to make everything balanced.

KEY POINTS

J.J Thomson's experiments with the cathode ray tubes showed that all atoms contained tiny negatively charged subatomic particles or electrons. Thomson also discovered electrons. Thomson's plum pudding model of the atom had negatively charged electrons embedded within a positively charged "soup". Rutherford's gold foil experiment showed that the atom is mostly empty space with a tiny dense, positively-charged nucleus. Rutherford proposed the nuclear module of the atom. Rutherford also discovered protons. James Chadwick discovered the neutrons.

18. Can atoms of two different elements have the same number of protons? Explain your answer.

No, the amount of protons in an single atom of that element identifies that element, so each element has a different amount of protons.

Alpha radiation

Radiation that is made up of alpha particles; is deflected toward a negatively charged plate when radiation from a radioactive source is directed between two electrically charged plates.

beta radiation

Radiation that is made up of beta particles; is deflected toward a positively charged plate when radiation from a radioactive source is directed between two electrically charged plates.

What led scientists to conclude that most of the atom's mass is concentrated in a very small nucleus? What particles are responsible for that mass?

Rutherford concluded from his metal foil experiments that most of an atom is empty space with a tiny, dense, positively charged nucleus at the center that contains most of the mass of an atom. Protons and neutrons are responsible for an atom's mass.

Dalton's Atomic Theory

States that matter is composed of extremely small particles called atoms; atoms are invisible and indestructible; atoms of a given element are identical in size, mass, and chemical properties; atoms of a specific element are different from those of another element; different atoms combine in simple whole-number ratios to form compounds; in a chemical reaction, atoms are separated, combined, or rearranged.

Nucleus

The extremely small, positively charged, dense center of an atom that contains positively charged protons and neutral neutrons.

Atomic Number

The number of protons in an atom.

17. Explain the relationship between the number of protons and the number of electrons in an atom of argon.

The number of protons will be the same number of electrons. Since Argon's atomic number is 18 and the atomic number equals the amount of protons, there are 18 protons and 18 electrons in an atom of Argon.

20. Explain the meaning of the number printed at the bottom of each box of the periodic table.

The number printed at the bottom of each box of the periodic table is the atomic mass. The atomic mass is the mass of a single atom of a chemical element. It includes the masses of the 3 subatomic particles that make up an atom: protons, neutrons, and electrons.

19. What particles make up the atom of selenium-80?

There are 34 protons, 34 electrons and 45 neutrons in an single atom of selenium-80.

8. Describe the subatomic particles comprising an isotope of zirconium- 94.

There are 40 protons, 40 electrons and 54 neutrons in an isotope of zirconium-94.

7. All naturally occurring atoms of fluorine have a mass number of 19. Determine the number of protons, electrons, and neutrons in an atom of fluorine and write the atom's symbol.

There are 9 protons, 9 electrons and 10 neutrons in fluorine. The atom's symbol is F.

9. An atom of a certain element has a mass of 112 and is known to contain 64 neutrons. Identify the atom and determine the number of protons and electrons the atom contains.

This atom has 48 protons, 48 electrons, 64 neutrons and has a mass number of 112. This atom is called Cadmium.

11. Gallium occurs in nature as a mix of two isotopes. They are Ga- 69 with a 60.108% abundance and a mass of 68.926 amu and Ga- 71 with a 39.892% abundance and an atomic mass of 70.925. Calculate the atomic mass of gallium.

To calculate atomic mass, the formula is --isotope 1-- (amu (atomic mass unit)) x (% abundance in decimal form) + --isotope 2-- (amu) x (% abundance in decimal form) + --isotope 3-- ... . So the math is (68.926 amu) x (0.60108) + (70. 925 amu) x (0.39892) = 69.723 amu

12. (isotope 1) Germanium-70 abundance(%): 21.23 Atomic Mass: 69.924 (isotope 2) Germanium-72 abundance(%): 27.66 Atomic Mass: 71.922 (isotope 3) Germanium-73 abundance(%): 7.73 Atomic Mass: 72.923 (isotope 4) Germanium-74 abundance(%): 35.94 Atomic Mass: 73.921 (isotope 5) Germanium-76 abundance(%): 7.44 Atomic Mass: 75.921 The following table shows the five isotopes of germanium found in nature, the abundance of each isotope, and the atomic mass of each isotope. Calculate the atomic mass of germanium.

To calculate atomic mass, the formula is --isotope 1-- (amu) x (% abundance in decimal form) + --isotope 2-- (amu) (% abundance decimal form) + --isotope 3-- ... . So the math is (69.924 amu) x (.2123) + (71.922 amu) x (.2766) + (72.923 amu) x (.0773) + (73.921 amu) x (.3594) + (75.921 amu) x (.0744) = 72.59 amu

The element chlorine occurs in nature as a mix of two isotopes. Chlorine-35 has an atomic mass of 34.969 amu and makes up 75.77% of chlorine atoms. Chlorine-37 atoms make up the remaining 24.23% of all chlorine. Use the average atomic mass of chlorine from the periodic table to calculate the atomic mass of chlorine-37 atoms.

To calculate atomic mass, the formula is --isotope 1-- (amu) x (% abundance in decimal form) + --isotope 2-- (amu) x (% abundance in decimal form) + --isotope 3-- ... . So the math is (34.969 amu) x (0.7577) + (36.967 amu) x (0.2423) = 54.453 amu

22. Complete the following table...

Type of Radiation: Beta * 1/1840 mass number *-1 charge *composition is electron Type of Radiation: Alpha * 4 mass number * +2 charge *composition are 2 protons and 2 neutrons Type of Radiation: Gamma *0 mass number *no charge *composition is energy only

beta particle

a high-speed electron with a 1- charge that is emitted during radioactive decay.

Electron

a negatively charged, fast-moving particle with an extremely small mass that is found in all forms of matter and moves through the empty space surrounding an atom's nucleus.

Neutron

a neutral, subatomic particle in an atom's nucleus that has a mass nearly equal to that of a proton.

nuclear equation

a type of equation that shows the atomic number and mass number of the particles involved.

21. Write the symbols for the following isotopes.

a. antimony-123: 123/51 Sb b. silicon-28: 28/14 Si c. mercury-199: 199/80 Hg **#/# MEANS 'OVER' , NOT 'DIVIDE'**

1. Electron matches to..

a. cathode ray, h. identified by Thomson, d. has a charge of 1-, g. equals to number of protons.

Theory

an explanation supported by many experiments; is still subject to new experimental data, can be modified, and is considered successful if it can be used to make predictions that are true.

2. How many electrons and protons are contained in an atom of each of the following elements? -arsenic -gold -fluorine -molybdenum -polonium -barium

arsenic- 33 electrons, 33 protons gold- 79 electrons, 79 protons fluorine- 9 electrons, 9 protons molybdenum- 42 electrons, 42 protons polonium- 84 electrons, 84 protons barium- 56 electrons, 56 electrons

Neutrons matches to..

b. discovered in 1932, e. has no charge and mass of 1 amu, I. symbolized by n^0.

Gamma Rays

high-energy radiation that has no electrical charge and no mass, is not deflected by electric or magnetic fields, usually accompanies alpha and beta radiation, and accounts for most of the energy lost during radioactive decay

Protons matches to..

j. has a positive charge and relative mass of 1.

Nucleus matches to..

k. the center of an atom, c. caused large deflections of alpha particles in Rutherford's experiment, f. contains nearly all of an atom's mass (gold foil experiment), j. site of an atom's positive charge.

Atomic Mass Unit (AMU)

one-twelfth the mass of a carbon-12 atom.

Cathode ray

radiation that originates from the cathode and travels to the anode of a cathode-ray tube.

Mass number

the number after an element's name, representing the sum of its protons and neutrons.

Atom

the smallest particle of an element that retains the properties of that element.

Atomic Mass

the weighted average mass of the isotopes of that element.

10. A neutral atom has 78 electrons and a mass number of 198. Identify the atom and determine the number of protons and neutrons in its nucleus.

this atom has 78 protons, 78 electrons, 120 neutrons and a mass number of 198. This atom is called Platium.