2.1.4 notes (Chapter 4)

4.2 The Structure of an Atom (p. 108)

Atom-basic building blocks of matter; smallest particle of an element

Nucleus-positively charged center of an atom; contains essentially all the mass of the atom

Symbol / Charge / Relative mass / Location
Proton / p+ / Positive (+) / 1 amu / Nucleus
Neutron / n0 / Neutral / 1 amu / Nucleus
electron / e- / Negative
(-) / 0 amu / Electron cloud

Atomic number-the number of protons in an atom’s nucleus

  • Same element = same # of protons
  • Example: All Carbon atoms have 6 protons
  • Different element = different # of protons
  • Example: All Carbon atoms have 6 protons while all Nitrogen atoms have 7 protons
  • In a neutral atom, the # of electrons = # of protons
  • In a neutral Carbon atom, there are 6 protons and 6 electrons
  • 6+ + 6- = 0
  • The atomic # is listed above the chemical symbol on periodic table

H = _____Zn = _____ Ca = _____Ne = _____ B = _____ Na =_____

Chemical symbol-an abbreviated way to write the name of an element

  • Consists of one capital letter or a capital letter plus one or two small letters
  • For example: Carbon = C; Hydrogen = H; Cobalt = Co
  • Also called element symbol

Mass number – the sum of the protons and neutrons in the nucleus of an atom

  • Protons and neutrons are the only parts of the atom that have mass
  • Electrons have no mass.

Number of neutrons = mass number – atomic number

  • For example:

Number of neutrons = mass number of carbon – atomic number for carbon

X = 14 – 6

X = 8 neutrons in C-14

Isotopes – atoms of the same element that have different numbers of neutrons; therefore, they have different mass numbers

  • Most elements have more than one isotope
  • With most elements, it is hard to notice any differences in the physical or chemical properties of their isotopes
  • Identify which isotope by using chemical name-mass number (i.e. O-16, O-17, O-18 or oxygen-16, oxygen-17, oxygen-18)
  • If you round the Atomic mass (number at the bottom on the periodic table), you will have the most commonisotope for that element
  • They use a weighted average of all known isotopes to calculate the atomic mass. That is why it is a decimal!

Chapter 4.3 Modern Atomic Theory (p. 113)

Energy Level: / Maximum number
of electrons:
1 / 2
2 / 8
3 / 18
4 / 32

Niels Bohr (1885-1962) developed a model of the atom in which the electrons move with constant speed in fixed orbits around the nucleus

  • Like planets around the sun
  • Electrons gain or lose energy when they move between fixed energy levels
  • Electrons cannot exist between the “rungs of the ladder”

Electron Cloud Model (p. 116)

  • Bohr was incorrect in assuming that the electrons moved like planets in the solar system
  • Electrons move in a less predictable way
  • Electron cloud model – a visual model of the most likely locations for electrons in an atom
  • The cloud is denser at locations where you are more likely to find electrons

Summary:

Protons are determined by the atomic number, which is the top number on the periodic table

Electrons are equal to protons in neutral atoms.

The bottom # is the atomic mass #, which is the average atomic mass of all the known isotopes for the element.

When you round the bottom you get the mass # and the most common isotope. Mass # = protons + neutrons.

So, neutrons are found by subtracting the atomic # (top #) from the mass # (bottom # rounded).

Isotopes have different numbers of neutrons, which causes them to also have a different mass.

Example of how to write isotopes: Carbon-12, C-12 or (see right)

Valence electrons are the electrons in the outer shell. They determine how reactive an element is.

Samples:

1. Why do atoms of elements have neutral charges?

a. all atoms contain neutrons which have no charge

b. the # of protons and neutrons are equal

c. the # of protons and electrons are equal

d. the # of neutrons and electrons are equal

2. What region of the atom determines the volume of the atom?

a. the nucleus b/c almost all the mass of the atom is located there

b. the nucleus b/c it is extremely dense

c. the electron cloud b/c it is extremely dense

d. the electron cloud b/c the volume of the nucleus is insignificant compare to the volume of the electron cloud

3. An isotope of chlorine has 17 protons and 19 neutrons. What is the mass # for that isotope of chlorine?

a. 2b. 17c. 19d. 36

4. How do isotopes of the same element differ?

a. they have the same # of protons and electrons but a different # of neutrons.

B. They have the same # of protons and neutrons but at different # of electrons

c. They have the same # of neutrons and electrons but a different # of protons.

D. They have different symbols

5. What is the reason for the difference in mass b/w fluorine-18 and fluorine-19?

a. F-18 has one less proton than F-19

b. F-18 has one less neutron than F-19.

c. F-19 has one more electron than F-18

d. F-19 has one more nucleus than F-18.

6. Which statement about molecules and atoms is true?

a. atoms are combinations of two or more molecules.

B. molecules are combinations of two or more atoms.

c. atoms in a molecule must all be different

d. molecules can never be separated into component parts

7. If an uncharged atom loses an electron, what will be the electrical charge of that atom?

a. +1b. +2c. –1d. –2

8. Which of the following subatomic particles contributes significantly to the mass of an atom but does not contribute to its electrical charge?

a. protonb. quarksc. electrond. neutron

9. Which term is correctly paired with its properties?

a. electron; negatively charged; mass = to a neutron

b. proton; positively charged; mass about = to an electron

c. neutron; no electric charge; mass about = to a proton

d. nucleus; no electric charge; mass about = to a neutron

10. How many protons are in the nucleus of a sodium atom? A. 11 b. 12 c. 23 d. 24

11. Which one best represents an isotope of potassium?

A. 20p, 20nb. 17p, 22nc. 18p, 21nd. 19p, 19n

12. Which ion would have a charge of –2?

A. 18e, 16nb. 10e, 8pc. 0e, 2pd. 6e, 8p

13. Which part of the atom has a positive charge?

a. protonsb. neutronsc. electronsd. electron shell

14. Which part of the atom has no charge?

a. protonsb. neutronsc. electronsd. the nucleus


15. Based on the diagram above, what is the atomic mass of this atom? A 3 b. 6 c. 9 d. 2

16. Which subatomic particles are found in the nucleus of an atom?

a. protons & electronsb. electrons & neutrons

c. protons & neutronsd. protons, neutrons & electrons

17. What is the maximum # of electrons that are contained in the 1st orbital? A. 1 b. 2 c. 8 d. 18

18. How many neutrons are in nitrogen-15?

A. 6b. 7c. 8d. 15

19. Lithium and helium are elements. Given this, what do you know about lithium and helium?

a. lithium is an isotope of helium

b. lithium has a dif # of protons than helium

c. lithium has a dif # of neutrons than helium

d. there are no atoms in lithium and helium

20. Which of the following in NOT a subatomic particle?

a. electronb. protonc. neutrond. atom

21. The easiest kind of electron to remove from an atom is

a. one that is not in an orbital

b. an electron from the 1st orbital

c. one that has particle-like properties

d. valence electron

22. How many protons are in hydrogen’s less common isotopes, H-2 and H-3?

a. 3 and 4 respectivelyb. 1 and 2 respectively

c. 2 and 3 respectivelyd. there is only one proton in each.

23. How many electrons are in an uncharged atom of beryllium-9? A. 4 b. 5 c. 9 d. 13

24. Oxygen-18 has how many neutrons?

A. 6b. 8c. 10d. 18

25. Determine the number of neutrons most copper atoms contain. A. 29 b. 35 c. 64 d. 34

26. Select the particle or particles that account for more than 99.99% of the mass of atoms other than hydrogen.

a. protons onlyb. electrons only

c. protons & neutronsd. electrons and neutrons

27. The nucleus of a tritium atom contains two neutrons and one proton. What is tritium?

a. an isotope of hydrogenb. an isotope of helium

c. an isotope of lithiumd. an ion of helium

28. Which two particles have approximately the same mass?

a. proton & electronb. proton & neutron

c. neutron and alpha particled. electron and alpha particle

29. When a potassium atom (K) forms a potassium ion (K+), the atom

a. gains a protonb. gains an electron

c. loses a protond. loses an electron

30. The nucleus of gold-198 contains

a. 79 protons and 119 neutrons

b. 79 protons and 118 neutrons

c. 79 protons and 79 electrons