High School Physical Science Mr. Brock Atoms and the Periodic Table High School Physical Science Mr. Brock

GPS Connections GPS Standards: S8P1 Students will examine the scientific view of the nature of matter. S8P1a: Distinguish between atoms and molecules. S8P1f: Recognize that there are more than 100 elements and some have similar properties as shown on the Periodic Table of Elements.

Atoms – the historical view The word "atom" comes from the Greek atomos and signifies "indivisible". This notion was invented by Leucippe of Milet in 420 BC. Democritus (c. 460 – 370 BC) promoted the theory that all nature could be understood in terms of the movement of atomos. In ancient times, many elements were known, including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb. The names of most of these are from the Latin words.

History of Atomic Theory John Dalton (1766-1844) proposed the Atomic Theory in 1803 which stated that: All matter is composed of atoms All atoms of the same element are identical Atoms of different elements are different Atoms unite in definite ratios to form compounds

History (continued) Dimitri Mendeleev’s periodic table (1869) classified and sorted elements based on common chemical properties. His table had 62 known elements, and left space for 20 elements that were not yet discovered. The elements were arranged in order of atomic number. The discovery of atoms to fill the blank spaces proved that his periodic table was a good model.

History (continued) The electron was discovered in 1897 by J.J. Thomson. He imagined the atom as a “raisin pudding” with electrons stuck in a cake of positive charge. In 1912, Ernest Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the Sun

History (continued) Rutherford also realized that the nucleus must contain both neutral and positively charged particles. From experiments, he concluded that the nucleus was a hard small sphere, and that most of the atom was empty space by how the alpha-particles behaved. The neutron was then discovered in 1932 by James Chadwick.

Vocabulary – Parts of an Atom Electron: negatively charged fundamental particle Proton: positively charged fundamental particle Neutron: uncharged fundamental particle Nucleus: small, central unit in the atom that contains neutrons and protons

Parts of an Atom Each element in the Periodic Table has a different number of protons in its nucleus Protons have positive charge Change the number of protons  change elements The element also has the same number of electrons Electrons have negative charge Change the number of electrons  ionize the element This is called chemistry Most elements also have neutrons Neutrons have no charge They are in the nuclei of atoms p e n

Atomic Structure Each atom is shown on the periodic table with clues to its atomic structure. Atomic Number (top) – tells how many protons (+) in an atom’s nucleus. Oxygen has 8 protons. Atomic Mass (bottom) – This is the average mass of an element’s atoms. It is equal to the combined total of neutrons & protons in an atom’s nucleus.

Determining Atomic Structure Protons: The atomic number tells number Neutrons: Subtract Atomic Number from Atomic Mass Electrons: Same number as Protons Oxygen Protons: 8 Neutrons: 16 – 8 = 8 Electrons: 8

Try this! Name: ? Symbol: ? How many: Protons ? Neutrons ? Electrons ?

Answers: Name: Fluorine Symbol: F How many: Protons: 9 Neutrons: 10 Electrons: 9

More questions: What is an element? Why are nuclei and atoms stable? What is a molecule?

Key Concepts and Vocabulary: Atoms, Elements and Molecules Atom: smallest unit of an element Element: any of more than 100 fundamental substances that consist of atoms of only one kind Molecule: a collection of atoms, bound together. Molecules can be made from only one element, such as H2 or O2 Molecules can be made from different elements, such as H2O or CO2

Isotopes A variant form of an element that has similar structure but different mass. Isotopes are atoms that have the same number of protons (atomic number is the same), but a different number of neutrons (atomic mass is different). If it looses protons, it becomes a different element. Each element has a limited number of isotopes that occur naturally. Some isotopes are unstable and radioactive.

Ions Ions are atoms with an electrical charge. This charge comes from either losing or gaining electrons. They have the same number of neutrons and protons. They carry an electrical charge.

History of the atom (Part 2) Following Ernest Rutherford’s planetary model of the atom, it was realized that the attraction between the electrons and the protons should make the atom unstable In 1913 Niels Bohr proposed a model in which the electrons would stably occupy fixed orbits, as long as these orbits had special locations.

History of the atom (continued) In the Bohr model, electrons occupy specific “orbits,” but can change orbits, accompanied by the absorption or emission of a photon of a specific color of light (remember this when we study light!)

History of the atom (continued) Modern theories lead to the theory that there are stable locations of electrons, which are not exact planetary orbits, but are characterized by specific numeric values. Each electron shell is characterized by a different principle quantum number, usually called n.

History of the atom (continued) In quantum theory, the electron shells are not fixed orbits, but clouds of probability. You can’t measure the exact location of the electron. Each electron orbital cloud has a different shape, and no two electrons can be in the same orbital (unless they have opposite spins.)

Periodic Table of the Elements Review: What are the numbers in each box?

Navigating the Periodic Table The rows (across) are the “periods” Each period starts a new shell of electrons The periods are numbered starting with 1 at the top The columns (up and down) are the “groups” Each group has similar chemical properties The groups are numbered starting with 1 at the left Elements with similar properties have the same number of electrons in the outermost shell (or orbital). These are called valence electrons.

Electron Shells & Atomic Structure The first shell will hold up to two electrons. The orbital is spherical, and called 1s. The first row of the periodic table consists of 2 elements with 1s electrons. Hydrogen has 1 electron in this shell, Helium has 2.

Electron Shells & Atomic Structure (continued) Atoms in the second (and third) rows of the Periodic Table each add up to eight electrons in “P” orbitals. The shells that are filled are made of a spherical orbital that holds 2 electrons, called 2s (second row) or 3s (third row), and 3 non-spherical orbitals that hold a total 6 electrons, called 2p (second row) or 3p (third row).

Electron Shells & Atomic Structure (continued) Look at a copy of the periodic table. The elements which have the same number of electrons in their outer orbitals (valence electrons), are in the same “family” and have similar characteristics, depending on the number. Group 1: 1 valence electron – Alkali Metals Group 2: 2 valence electrons – Alkali Earth Metals Group 17: 7 valence electrons – Halogen Family Group 18: 8 valence electrons (2 Helium – outer shell is filled) – Noble Gases

Shell structure Carbon=C Sodium=Na Neon=Ne Chlorine=Cl p e Carbon=C Sodium=Na Neon=Ne Chlorine=Cl How many protons and electrons do these elements have? How many orbitals? How many electrons in each? How many valence electrons? Review: what is this element?

Shell structure: thinking deeper Atoms with full outer shells are the most stable. They do not gain or lose electrons easily. Where are the elements with very stable outer shells in the periodic table? Atoms will combine best in ways that make them more stable – fill their outer shells. This is called “valence”or chemical bonding. The two ways this can occur are by: Ionic bonding – transferring electrons Covalent bonding – sharing electrons Look at your periodic table. Notice the number of valence electrons in each family. How will atoms most likely combine to become stable?

Key concepts: Periodic Table The number of elements in each of the rows (periods) in the periodic table, are due to the rules that relate to the electron orbitals. In columns (groups) in the periodic table, similar chemical properties are due to the number of valence electrons in filled or unfilled shells. Completely filled shells make an atom very stable Elements with 1 or 2 electrons outside of filled shells or with 1 or 2 missing electrons are very chemically reactive. They always try to combine with other elements that can fill their shells.

Important Dates Tuesday 8/23 Notes Quiz-you will need your device Tuesday 8/23 Begin “Periodic Table Basics Project”-Due on Friday 8/26 Wednesday 8/24 Vocabulary Quiz- you will need you device Friday 8/26 What kind of Families are in the neighborhood project poster introduction