Properties of Atoms and the Periodic Table Chapter 18 Properties of Atoms and the Periodic Table

Scientific Shorthand Scientists use abbreviations to write the name of elements. Abbreviations are easier to write than the whole element. For example: Carbon is written as Aluminum is written as Silver is written as C Al Ag

Scientific Shorthand The first letter in the symbol is ALWAYS written with a capital letter. If there is a second letter, it is ALWAYS written as a lowercase letter. Some element symbols are based on their English names, while others are based on their Latin names. Silver is Ag from its Latin name Argentum.

Atoms Elements are made of atoms Atoms are the smallest piece of matter that still retains the properties of the element.

Subatomic Particles Each atom is made up of smaller particles. In the center of the atom is the nucleus. The nucleus is made of protons and neutrons.

Subatomic Particles Each atom is made up of smaller particles. Electrons orbit around the nucleus

Subatomic Particles Properties of Protons Properties of Neutrons Electrical charge of +1 Mass =1 amu. Properties of Neutrons Electrical charge of 0. Properties of Electrons Electrical charge of -1 Mass is approximately 1/1800 of a proton.

Quarks Protons, neutrons and electrons are all made up of even smaller particles called quarks.

Quarks To study quarks, scientists smash atoms together to break the protons apart.

Quarks Based on the data collected, they can reconstruct the structure of the atom.

The Atomic Model - History Democritus (400 B.C.) First proposed that atoms made up all substances. Aristotle Believed that matter is uniform throughout. This idea lasted for about 2,000 years.

The Atomic Model - History Dalton’s Model Each atom was a solid sphere. Allowed scientists to explain how chemical reactions occurred. Thomson, Rutherford, and Bohr Each scientist’s experiments helped to identity different parts of the atom and the structure of the atom.

Atomic Model

Electron Cloud Model The most current model of the atom. The electron cloud is 100,000 times larger than the diameter of the nucleus, but each electron is smaller than the proton. Electrons are so small, and moving so fast, that they are difficult to find.

What holds the Nucleus Together? Protons in the nucleus both repel and attract each other. The repulsions are due to electromagnetic force and the attractions are due to the strong nuclear force. The strong nuclear force only acts over very short distances, about the size of an atomic nucleus. Neutrons and protons also attract each other because of the strong nuclear force.

Atomic Masses Most of the mass of an atom is within the nucleus. Protons and neutrons each weigh about 1.6726 x 10-24 kg. That’s 0.000 000 000 000 000 000 000 001 672 6 kg! Electrons are 1/1800 of the mass of a proton or neutron.

Atomic Masses To measure atomic mass, we use the “atomic mass unit” or amu. Mass of 1 proton = 1 amu Mass of 1 neutron = 1 amu

Atomic Number The number of protons in an atom identify the element. Each element has a different number of protons. Atoms with 8 protons are always oxygen. Atoms with 6 protons are always carbon. Atoms with 16 protons are always sulfur. The number of protons in an atom is called the atomic number.

Atomic Number Practice Use your periodic table to find the atomic number of the following elements: Aluminum (Al) Titanium (Ti) Tin (Sn) Osmium (Os) Erbium (Er) How many protons does each atom have? The number of protons are equal to the atomic number. Al = 13 Ti = 22 Sn = 50 Os = 76 Er = 68

Mass Number The mass number of an atom is the sum of the number of protons and neutrons in the nucleus. Element Protons Neutrons Mass Number Boron 5 6 Carbon Oxygen 8 Sodium 11 12 Copper 29 34 5+6 11 6+6 12 8+8 16 11+12 23 29+34 63

Using the Atomic Number & Mass Number If you know the atomic number and mass number, you can determine the number of neutrons. Mass Number - Atomic Number Number of Neutrons

Practice Determine the number of protons and neutrons in the following atoms: Lithium – Atomic Number = 3 Mass Number = 7 Argon – Atomic Number = 18 Mass Number = 39 Strontium – Atomic Number = 38 Mass Number = 88

Answers Determine the number of protons and neutrons in the following atoms: Lithium – Protons = 3 Neutrons = 7 – 3 = 4 Argon – Protons = 18 Neutrons = 39 – 18 = 21 Strontium – Protons = 38 Neutrons = 88 – 38 = 50

Isotopes Atoms of one type of element must have the same number of protons. However, they can have different numbers of neutrons. Atoms with the same number of protons and different numbers of neutrons are called isotopes.

Isotopes Examples Carbon-12 has a mass of 12 amu. All carbon atoms must have 6 protons. Neutrons = 12 – 6 = 6. C-12 has 6 protons and 6 neutrons. Carbon-14 has a mass of 14 amu. Neutrons = 14 – 6 = 8. C-14 has 6 protons and 8 neutrons.

Isotopes Examples Uranium-235 has a mass of 235 amu. All uranium atoms must have 92 protons. Neutrons = 235 – 92 = 143. U-235 has 92 protons and 143 neutrons. Uranium-238 has a mass of 238 amu. Neutrons = 238 – 92 = 146. U-238 has 92 protons and 146 neutrons.

Average Atomic Mass Because atoms can have different numbers of neutrons, the mass numbers can be different. To get an overall mass of one element, we take the weighted-average of all the isotopes and determine the average atomic mass for the element.

Neutral Atoms In the nucleus, which particles have charge? Protons What charge do they have? Positive What particle is opposite that charge? Electrons

Neutral Atoms To balance the charges in the atom, the number of protons must equal the number of electrons. Li has 3 protons, so the nucleus has a charge of +3. To balance that charge, there must be 3 electrons that add up to -3. Overall, the charge is (+3) + (-3) = 0, so the atom is neutral.

Practice Determine how many electrons the following atoms have: Magnesium, Protons = 12 Beryllium, Protons = 4 Nitrogen, Atomic Number = 7 Bromine, Atomic Number = 35 12 Electrons 4 Electrons 7 Electrons 35 Electrons

Practice Iodine I 53 127 Mercury Hg 80 201 Neon 10 20 Mg 12 Rb 37 48 Element Symbol Atomic Number Mass Number Protons Neutrons Electrons Iodine I 53 127 Mercury Hg 80 201 Neon 10 20 Mg 12 Rb 37 48 41 51 75 111

Practice Iodine I 53 127 74 Mercury Hg 80 201 121 Neon Ne 10 20 Mg 12 Element Symbol Atomic Number Mass Number Protons Neutrons Electrons Iodine I 53 127 74 Mercury Hg 80 201 121 Neon Ne 10 20 Magnesium Mg 12 24 Rubidium Rb 37 85 48 Niobium Nb 41 92 51 Rhenium Re 75 186 111

Bohr Models of the Atoms Each atom had orbitals or shells in which the electrons can fit. 1st Shell: up to 2 electrons can fit 2nd Shell: up to 8 electrons can fit 3rd Shell: up to 18 electrons can fit 4th Shell: up to 32 electrons can fit Must start with the smallest/closest orbital or shell first.

Drawing Bohr Models Hydrogen Boron AN = 1 AM = 1 e- = 1 AN = 5 AM = 11 1 p+, 0 no AN = 1 AM = 1 e- = 1 5 p+, 6 no Boron AN = 5 AM = 11 e- = 5

Drawing Bohr Models Chlorine AN = 17 AM = 35 e- = 17 17 p+, 18 no

Electron Dot Diagrams Write the symbol of the element Determine the number of valence electrons (electrons in the outermost energy level) Start placing valence electrons around the symbol Pair electrons only after all four sides (top, bottom, left, right) have been used once

H H H H Example: Hydrogen Hydrogen has 1 valence electron Chose one side, and place the electron H H H H OR OR OR

Cl Example: Chlorine Chlorine has 7 valence electrons Place one on each side first Then begin to pair the remaining electrons Cl

N Example: Nitrogen Nitrogen has 5 valence electrons Place one on each side first Then begin to pair the remaining electrons N

Be Example: Beryllium Beryllium has 2 valence electrons Place each electron on different sides Be

He Example: Helium Helium has 2 valence electrons Helium is an EXCEPTION Pair the two electrons because the energy level can only 2 electrons He

Periodic Law Scientists Julius Lothar Meyer and Dmitri Mendeleev individually produced classification schemes for elements in 1869. Periodic Law: When elements are arranged in order of increasing atomic numbers, elements with similar chemical properties will occur at regular (periodic) intervals.

Periodic Table The rows on the periodic table are separated into periods.

Periodic Table As chemists worked on determining which substances were elements, they noticed that some elements acted very much like other elements. For example, one atom of some metals always reacts with two atoms of oxygen. Chemists called these similar elements a group of elements.

Periodic Table

Regions of the Periodic Table Metals: Elements to the lower left side of the periodic table. Nonmetals: Elements to the upper right of the periodic table. Metalloids: Elements in between the metals and nonmetals.

Metalloids 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Metals 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Hydrogen is an exception

Nonmetals 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Hydrogen is an exception