Welcome to Discovery Education Player The Atom Welcome to Discovery Education Player

What is an element? What are the subatomic parts of an atom?

An atom Basic unit of matter, “unable to be cut” Element Pure substance entirely of one atom

What are the Subatomic Particles? Name three and their charges? Proton Neutron Electron

The Atom Cloud of negative Electrons charge (2 electrons) Nucleus (a) (b) Cloud of negative charge (2 electrons) Electrons

Who is Neils Bohr? He proposed a theory stating: an atom is composed of a dense nucleus with electrons in its surrounding orbit The electrons must have a certain amount of energy to orbit the nucleus. Suggests that electrons more in a fixed manner around the nucleus.

Modern Atom Model Electron cloud model Protons have a mass: 1.67 x 10-24 g Mass is so small, units atomic mass unit (1 amu) Atomic number: number of protons, of the same element the protons must be the same Electrons: are equal to but have an opposite charge to that of a proton Less mass 1/1836 amu Mass number: sum of the protons and neutrons

Atomic Structure 15 7N Mass number = protons plus neutrons If mass number is 15, how many protons do you have if you have 8 neutrons? Atomic number = number of protons * If the atom is neutral the protons and electrons are equal! If the mass number is 15 and there is no charge and the atomic number is 7 how many electrons and neutrons do you have?

Atomic Structure Continued!! Atomic Number The number of protons in the nucleus of an atom Determines which element Mass Number The number of nucleons (protons + neutrons) If you don’t know the mass number you can round off the atomic mass for that element # neutrons = mass # - atomic # The atomic number cannot change. Mass number can.

Element Atomic Number Atomic Mass Mass # Protons Neutrons Electrons

Element Atomic # Atomic Mass Mass Number Protons Neutrons Electrons

Each electron in an atom has its own distinct amount of energy. When electrons are in their lowest energy state, it is called the ground state The ground state for Na is 2-8-1

Tom Lehrer's "The Elements" Tom Lehrer's "The Elements". A Flash animation by Mike Stanfill, Private Hand

II. Periodic Table

elements: Periodic Table are arranged in increasing atomic number. Placement or location of elements on the Periodic Table indicates the physical and chemical properties of that element. Number of protons in an atom (atomic number) identifies the element Atomic mass: found on the Periodic Table of the Elements

Classifying Elements Nonmetals on the right Metals on the left metalloids or semimetals (B, Si, Ge, As, Sb, Te), noble gases Nonmetals on the right Metals on the left Metalloids semimetals

Average atomic mass of an element Average atomic mass of an element . . . - the weighted average of the masses of its naturally occurring isotopes Isotope Mass Abundance Calculation 12C 12 98.89% 12 x .9889 = 11.87 13C 13 1.108% 13 x 0.01108 = 0.1440 Atomic Mass (weighted average) 12.01 amu

Isotopes C-12 isotope C-13 isotope C-14radioactive Isotope: identified by the sum of the protons and neutrons in an atom = (mass number) Isotope: atom of the same element having same number of protons but different number of neutrons 14C, carbon-14, C-14 C-12 isotope C-13 isotope C-14radioactive

Density=mass/volume A physical property is one which does not change the identity of the substance when tested.

Differentiation of Elements physical properties differentiate elements by their Physical properties ex: density, conductivity, malleability, solubility, and hardness, differ Elements can be differentiated by chemical properties too. Chemical properties describe how an element behaves during a chemical reaction. When testing a chemical property, the substance may change into another substance.

Buckminsterfullerene Some elements exist in two or more forms in the same phase. These forms differ in their molecular or crystal structure, and hence in their properties. These are called allotropes. Allotropes of oxygen Allotropes of carbon Oxygen ( O2 ) Graphite Ozone ( O3 ) Diamond Buckminsterfullerene

allotropes Some elements exist in two or more forms of the same phase. They differ in molecular or crystal structure, and in properties.

Comparing the physical properties of metals and nonmetals Many different colors Sulfur – yellow Chlorine – green Bromine – orange Iodine - purple Many different states (phases) H, N, O – gas Br – liquid S, C, I – solid Poor conductors of heat and electricity (except carbon) Brittle – breaks when hit Silvery gray color except copper and gold Solid at room temperature except mercury Good conductors of heat and electricity Malleable – can be hammered into shapes (thin sheets) Ductile – can be pulled into wires

All elements are solid at room temperature except for the following: Liquids Mercury (Hg) - the only liquid metal at room temperature Bromine (Br) - the only liquid nonmetal at room temperature Gases Hydrogen (H) Oxygen (O) Nitrogen (N) Fluorine (F) Chlorine (Cl) All of group 18 (noble gases) Helium (He), Neon (Ne) Argon (Ar), Krypton (Kr), Xenon (Xe), Radon (Rn)

For Groups 1, 2, and 13-18 on the Periodic Table, elements within the same group have the same number of valence electrons (helium is an exception) and therefore similar chemical properties.

Group numbers and family names Group 1 Alkali Metals Very reactive metals, always found as compounds in nature 1 valence electron - lose 1 electron to form +1 ions Group 2 Alkaline Earth Metals Reactive metals, always found as compounds in nature 2 valence electrons - lose 2 electron to form +2 ions Group 17 Halogens Reactive nonmetals 7 valence electrons - gain 1 electron to form –1 ions Groups 18 Noble Gases Not reactive – do not form ions Filled, stable valence shell (8 electrons except He which has 2)

The succession of elements within the same group demonstrates characteristic trends: differences in atomic radius, ionic radius, electronegativity, first ionization energy, metallic/nonmetallic properties. Going down a group, there are more shells separating the nucleus from the valence electrons

Reference Table S

Trends in Atomic Radius Atomic Radius – half the distance between two nuclei Going down a group, the atomic radius increases because there are more principal energy levels (shells) Going across a period, the atomic radius decreases because there are more protons pulling the valence shell closer

Atomic Radius

The succession of elements across the same period demonstrates characteristic trends: differences in atomic radius, ionic radius, electronegativity, first ionization energy, metallic/nonmetallic properties. Going across a period, there are more protons pulling on the valence electrons

Forming Ions – making atoms happy Atoms gain or lose electrons to complete their outer shell A noble gas configuration A complete octet 8 electrons Metals lose electrons to form positive (+) ions Nonmetals gain electrons to form negative (-) ions Ionic Radius A negative ion is always larger than its original atom. A positive ion is always smaller than its original atom.

Ionic Radius in Metals Sodium (Na) is a metal Electron configuration 2-8-1 (11 protons and 11 electrons) Loses 1 electron in its valence shell A sodium atom becomes a sodium ion Na+ 2-8 (10 electrons but 11 protons) Same electron configuration as a noble gas (Ne) but has more protons. Electrons are pulled in much closer so the radius decreases. 2+ ions are even smaller than + ions

Ionic Radius in Nonmetals Notice-name of negative ions end in IDE Chlorine (Cl) is a nonmetal Electron configuration 2-8-7 (17 protons and 17 electrons) Gains 1 electron in its valence shell A chlorine atom becomes a chloride ion Cl- 2-8-8 (18 electrons but only 17 protons) Same electron configuration as a noble gas (Ar) but has fewer protons. Electrons repel each other and the radius increases. 2- ions are even larger than – ions