Ch. 2: Atoms, Ions, and Molecules

Radioactivity:

the spontaneous emission of high-energy radiation and particles

Do elements in the same column share (periodic table)

similar chemical properties

Why did Thomson’s discovery of the electron lead others to propose that a positive particle might exist within the atom?

Matter is neutral, so some positive particle must be present to provide electrical neutrality

Who created the Cathode Ray Tube (CRT)

Joseph John Thomson

after electricity passes through a CRT what does it transform into

Cathode rays

Due to Cathode rays being invisible how where they made visible

coat the opp. end of CRT with phosphorescent material = glow (after beam hits)

What evidence (using the CRT) is given for the idea that cathode rays aren't energy but negatively charged particles (electrons)

Cathode-ray beams are deflected by magnetic fields and electric fields

How where the cathode rays balanced

Adjusting the strength of electric/magnetic fields

What evidence is there for electrons being fundamental particles present in all forms of matter

Particles always behaved the same way

Particles always had the same mass to charge ratio

Based on the oil drop experiment what percentage was the concluded charge of a electron out of the modern value

1%

What is the modern measured value of an electrons charge

1.602 x 10^{-19} C

What is the SI unit for energy

C = coulomb

Mass of electron

9.109 x 10^{-28}g

How did Rutherford figure out that protons where part of the nucleus

Rutherford: Bombarding elements with (𝛂)particles = change(transmute)

• Hydrogen nuclei sometimes produced (transmutation Rxn)

  • Conclusion

    • Hydrogen Nuclei = proton = part of all nuclei

What charge do neutrons have

neutral particles

What’s the symbol for a neutron

n^0

Neutron (in atomic mass units (u))

1.00867 = 1

What’s the symbol for a proton

p^1

What’s the symbol for a electron

e^-1

Proton (in atomic mass units (u))

1.00728 = 1

Electron (in atomic mass units (u))

5.485799 × 10^-4 = 0

Neutron (in grams (g))

1.67493 x 10^-24

Proton (in grams (g))

1.67262 = 10^-24

Electrons (in grams (g))

9.10939 = 10^-28

Neutron (relative value)

0

Proton (relative value)

1+

Electron (relative value)

1-

Neutron (change (Celsius))

0

Proton (change (Celsius)(Charge))

+1.602 = 10^-19

Electron (change (Celsius)(Charge))

-1.602 = 10^-19

Units of mass for Subatomic particles

unified atomic mass units(u) or Daltons (Da)

In terms of carbon what does 1 u equal

1/12 the mass of carbon atom that has six protons and neutrons int its nucleus

In terms of grams what does 1 u equal

1.66054 x 10^{-24}g

State John Dalton’s atomic theory

1. Each element consists of atoms

   • atom = indestructible particles

     • not indestructible

2. Atoms of an element =

   • identical

     • Not quite identical

   • dif. from atoms of other elements

3. Atoms = Combine in simple ratios of whole numbers to form compounds

4. Atoms =

   • do not(chem. rxn)…

     • change

       • can change in nuclear rxns

     • created

     • destroyed

   • rxn → only changes arrangement in which atoms are bond

What was incorrect in John Daltons atomic Theory

• Each element consists of atoms

  • atom = indestructible particles (incorrect)

    • not indestructible (correct)

• Atoms of an element =

  • identical (incorrect)

    • Not quite identical (correct)

• Atoms =

  • do not(chem. rxn)…

    • change (incorrect)

      • can change in nuclear rxns (correct)

The radioactive atoms measured in the Baby Tooth Survey were strontium-90. Only one of the nuclides below is an isotope of strontium. Which one is it and why?

^{^87_38 X ^90_40 X ^234_90 X}

^87_38X is an isotope of strontium because its atomic number is 38 (each of its nuclei contains 38 protons). ^90_40X is an isotope of zirconium with a mass number of 90 (40 protons, 50 neutrons), and ^234_90X is an isotope of thorium because it has an atomic number of 90.

Write symbols in the form ^A_ZX for the nuclides that have (a) 6 protons and 6 neutrons, (b) 11 protons and 12 neutrons, and (c) 92 protons and 143 neutrons.

A. ^12_6 C

B. ^23_11 Na

C. ^235_92 U

Use the format A^X to write the symbols of the nuclides having (a) 26 protons and 30 neutrons, (b) 7 protons and 8 neutrons, (c) 17 protons and 20 neutrons, and (d) 19 protons and 20 neutrons.

a. 56^Fe

b. 15^N

c. 37^Cl

d. 39^K

How many neutrons are in each of the following nuclides: (a) 14^N; (b) 32^P; (c) 157^Gd?

a. 7

b. 17

c. 93

Determine the number of protons and neutrons in each of these radioactive nuclides: (a) 60^Co, used in cancer therapy; (b) 131^I, used in thyroid therapy; (c) 192^Ir, used to treat coronary disease.

.(a) 27 p, 33 n; (b) 53 p, 78 n; (c) 77 p, 115 n

During Francis W. Aston experiment on positively charged particles what was the difference between a cathode ray and a positive ray

• Modified cathode ray tubes(mostly evacuated) + fill gases(ex. neon)= conventional beams of cathode rays and 2ndary beams of positively charge particles

  • Cathode ray: streams of electrons that all have the same mass and charge regardless of the cathode material/fill gas

    • Positive rays: masses(particles) depend on the identity of the fill gas

Why are positive rays dependent on the identity of the fill gas?

• Not individual protons

• Rather… atoms of the fill gas that had lost electrons to form positively charge ions

Positive ray analyzer (type A)

A

What idea did Francis W. Aston’s experiment(positive rays) contradict?

contradicted the idea that each element was composed of the identical atoms (each have the same mass)

From Francis W. Aston’s experiment(positive rays) what where the resulting findings form the neon atoms

• Neon consists two kinds of isotopes

  • Isotopes of neon

    • Both:

      • same number of protons (10)

    • Iso(1):

      • 10 neutrons

        • Total mass = 20 u

    • Iso(2):

      • 12 neutrons

        • Total mass: 22u

Do atoms of the same element differ in protons or in neutrons

protons

do atoms of the same element differ in mass

yes

what determines the atomic number(Z)

number of protons

what identifies the atom of a element

number of protons

what is the periodic table ordered by?

atomic number

What defines the mass number(A)

Number of Nucleons(in the nucleus)

Nucleon

neutrons and protons

What defines an isotope (in terms of atomic number and mass numbers)

same atomic number(Z) + different mass numbers

What makes a neutral atom?

#electrons = #protons

Nuclide

specific combination of neutrons and protons (atom)

What’s the symbol for a nuclide

^A_Z X

Within a nuclide symbol what does A represent? ^A_Z X

A = # neutrons

Within a nuclide symbol what does Z represent? ^A_Z X

• Z = # protons (Often omitted due to X)

  • Ex. ^A X​

    • Written = neon-20 and neon-22

Within a nuclide symbol what does X represent? ^A_Z X

X = one/two letter for the element

• Ex. ^20_10Ne ^22_10​Ne ​

A

87.6169 u

Silver (Ag) has two stable isotopes: silver-107 (106.905 u) and silver-109 (108.905 u). If the average atomic mass of silver is 107.868 u, what is the natural abundance of each isotope? (Hint: Let x be the natural abundance of one of the isotopes. Then 1 2 x is the natural abundance of the other.)

^107Ag = 51.85%; ^109Ag = 48.15%

Atomic wt

weighted average of the masses of all isotopes of the element

Natural Abundances

the relative proportion (percentage or fraction) of each isotope of a chemical element as it is found in nature, before any artificial enrichment or depletion, used to calculate the element's average atomic mass on the periodic tabl

What’s the equation for determining the Atomic wt of an element

m_x = a₁m₁ + a₂m₂ + a₃m₃ + …..

in the following equation(atomic wt) (m_x = a₁m₁ + a₂m₂ + a₃m₃ + …..) what does m_x represent

average atomic mass of element (X)

in the following equation(atomic wt) (m_x = a₁m₁ + a₂m₂ + a₃m₃ + …..) what does m₁ represent

masses of isotopes

in the following equation(atomic wt) (m_x = a₁m₁ + a₂m₂ + a₃m₃ + …..) what does a₁ represent

natural abundances (decimal form)

What causes Isotopic abundances of elements to slightly vary

• the origins of samples

• the presence of certain other elements in them

Why did Mendeleev skip cells in his periodic table?

Because sometimes the next heaviest element that was known in the early 1870s did not have chemical properties similar to the other elements in the next column to be filled. For example, the next heaviest element after calcium (a group II element in Mendeleev’s table) was titanium, whose properties fit those of the elements in group IV, not group III. So, Mendeleev skipped the cell in group III and placed titanium in group IV. The missing group III element, scandium, was discovered (by a Scandinavian chemist) in 1879.

Use the periodic table on the inside front cover to determine the symbol and name of

each of the following elements:

a. The third-row element in group 14

b. The fourth-row alkaline earth metal

c. The halogen with fewer than 16 protons in its nucleus

(a) Si, silicon; (b) Ca, calcium; (c) F, fluorine.

Write the symbol and name of each element:

a. The metalloid in group 15 closest in mass to the noble gas krypton

b. The element in the fourth row that is an alkali metal

c. The transition metal in the fifth period with chemical properties most like those of zinc (Z = 30)

d. The nonmetal in the fourth period with chemical properties most like those of sulfur

. a. As, arsenic

b. K, potassium

c. Cd, cadmium

d. Se, selenium