Unit 3 – Atoms, Ions, Isotopes www.lab-initio.com

Conclusions from the Study of the Atom (so far…) Atom – smallest particle of an element that retains the properties of the element. Composed of 3 subatomic particles: Electrons Protons neutrons

Conclusions from the Study of the Atom (continued) Helium-4 Nucleus - small, dense center of an atom that contains nearly all of the atom’s mass Most of the mass of the atom is in the nucleus Most of the volume of the atom is empty space https://www.youtube.com/watch?v=addK0b2Isw8 Image: User Yzmo Wikimedia Commons.

amu: atomic mass unit. 1 amu = 1.67 x 10 g Atomic Particles Particle Charge Location Mass (amu) Mass (g) Electron, e- -1 Electron cloud ~0 9.11 x 10–28 Proton, p+ +1 Nucleus 1 1.67 x 10–24 Neutron, n0 amu: atomic mass unit. 1 amu = 1.67 x 10 g

Protons and neutrons are made of quarks. 4.2 https://www.youtube.com/watch?v=yQP4UJhNn0I Protons and neutrons are made of quarks. Electrons cannot be divided into smaller particles (as far as we know so far…..)

Identifying Atoms PROTONS determine the identity of the atom. 1 proton = Hydrogen 2 protons = Helium 6 protons = Carbon ISOTOPES are atoms of the same element with different numbers of neutrons. Carbon-12 has 6 protons + 6 neutrons Carbon-13 has 6 protons + 7 neutrons

Isotopes Isotopes are atoms of the same element with different numbers of neutrons. Isotope Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

Atomic Number Atomic number Atomic number of an element is the number of protons in the nucleus of each atom of that element. In a NEUTRAL atom, the atomic # is also the number of electrons. Atom p+ n0 e- Mass # Oxygen 10 33 42 15 31 8 8 Arsenic 33 Phosphorus 15

Mass Number Mass # = p+ + n0 Mass number is the number of protons and neutrons in the nucleus of an isotope. It is NOT on the periodic table. Mass # = p+ + n0 Atom p+ n0 e- Mass # Oxygen 10 33 42 15 8 8 18 Arsenic 33 75 Phosphorus 16 15 31

Isotope Naming HYPHEN NOTATION Hydrogen-3 Element name and the mass number NUCLEAR NOTATION 𝟑 𝑯 or 𝟏 𝟑 𝑯 Element symbol and mass number (top) and atomic number (bottom)

Isotopes - Naming How would you write Uranium-235 using the symbol? (atomic number = 92)

The total number of protons REVIEW: Atomic Number: The total number of protons Atomic number = # protons = # electrons Mass Number: The total number of protons and neutrons in a specific atom Mass number = # protons + # neutrons

Ions IONS - atoms that have gained or lost electrons Charged particles because unequal number of p+ and e- Metals lose electrons to form CATIONS (positively charged ions) Non-metals gain electrons to form ANIONS (negatively charged ions) A Negative ION

Practice Find the number of protons, neutrons & electrons: p+ n0 e- 23Na+ 11 12 10   16O2– 8 8 10 12C 6 6 6

Average Atomic Mass All isotopes of an element do not exist in equal abundance in the world Percent abundance in world: 90.48% 0.27% 9.25%

Atomic Mass Atomic Mass = weighted average of mass #’s of all isotopes Atomic number Atomic Mass = weighted average of mass #’s of all isotopes (ON the periodic table) Atomic mass Atomic Mass= % abundance mass # + % abundance mass # +… 100 Atom Mass # Percent Abundance Carbon-12 12 98.89 Carbon-13 13 1.11 Carbon-14 14 0.01 𝟗𝟖.𝟖𝟗 𝟏𝟐 + 𝟏.𝟏𝟏 𝟏𝟑 +(𝟎.𝟎𝟏)(𝟏𝟒) 𝟏𝟎𝟎 =𝟏𝟐.𝟎𝟏 amu

Neon-20 Neon-21 Neon-22 Calculate the average atomic mass of Neon 20.0 Example #1 Calculate the average atomic mass of Neon Atomic Mass= % abundance mass # + % abundance mass # +… 100 Isotope Mass (amu) (M) Percent abundance (P) Neon-20 20.0 90.48% Neon-21 21.0 0.27% Neon-22 22.0 9.25% 90.48 20.0 + 0.27 21.0 + 9.25 22.0 100 = 20.2 amu

Atomic Mass Neon-20 Which isotope is most abundant? If Neon has 3 isotopes: Neon-20, Neon-21, Neon-22, Weighted average atomic mass is 20.2 amu.

Example #2 Calculate the average atomic mass of Lithium Isotope Mass (amu) (M) Percent abundance (P) Lithium-6 6.01 7.5% Lithium-7 7.01 92.5% 7.5 6.01 + 92.5 7.01 100 = 6.94 amu

Cesium-132 Cesium-133 Cesium-134 Example #3 Calculate the average atomic mass of Cesium Isotope Mass (amu) (M) Percent abundance (P) Cesium-132 132.0 75.0% Cesium-133 133.0 20.0% Cesium-134 134.0 5.0% 75.0 132.0 + 20.0 133.0 + 5.0 134.0 100 = 132.3 amu

Questions 1) What particles make up an atom? Protons, Neutrons and Electrons 2) What are the charges on these particles? Protons (+1), Neutrons (none), Electrons (-1) 3) What particles make up the nucleus? Protons and Neutrons 3) What is the mass number? Mass of a specific atom = # p+ + # n0

More Questions: Atomic Number tells us: Atomic Mass tells us: The identity of the element; the number of protons (and electrons in a neutral atom) Atomic Mass tells us: The average mass in amu of all naturally occuring isotopes Mass