Chapter 15 – Elements & The Periodic Table 15.1 The Periodic Table of the Elements– (pp. 334-340)

Periodic Table Timeline Lavoisier (1770-1789) Composed the first list of 33 elements. Distinguished metals from nonmetals. Berzelius (1828) Created a table of atomic weights. Introduced idea of chemical symbols. Dobereiner (1829) Developed triads-groups of 3 elements with similar properties.

Newlands (1864) Arranged known elements in order of increasing atomic weights. Proposed the Law of Octaves. Meyer (1869) Compiled a periodic table with elements arranged by atomic weight. Elements with similar properties arranged in columns. Mendeleev (1869) Created a periodic with elements arranged by atomic weight. Elements with similar properties arranged in columns.

Ramsay (1894) Discovered noble gases. Moseley (1914) Determined atomic numbers of each element. Modified the periodic law-an element’s properties varies periodically with its atomic numbers. Seaborg (1940) Synthesized elements beyond uranium.

15.1 Physical properties Characteristics that you can see through direct observation are called physical properties. Physical properties include color, texture, density, brittleness, and state (solid, liquid, or gas). Melting point, boiling point, and specific heat are also physical properties. 5

15.1 Physical properties A physical change does not result in a new substance being formed. 6

15.1 Chemical properties Properties that can only be observed when one substance changes into a different substance are called chemical properties. Any change that transforms one substance into a different substance is called a chemical change. 7

15.1 The Periodic Table The periodic table organizes the elements according to how they combine with other elements (chemical properties). The periodic table is organized in order of increasing atomic number. 8

15.1 The Periodic Table The periodic table is further divided into periods and groups. Each horizontal row is called a period. Each vertical column is called a group or family. 9

15.1 Atomic Number Remember, the atomic number is the number of protons all atoms of that element have in their nuclei. This number does not change for that element. If the atom is neutral, it will have the same number of electrons as protons.

15.1 Atomic Mass The mass of individual atoms is so small that the numbers are difficult to work with. To make calculations easier, scientists use the atomic mass unit (amu). The atomic mass of any element is the average mass (in amu) of an atom of each element.

15.1 Atomic Mass Atomic masses differ from mass numbers because most elements in nature contain more than one isotope.

15.1 The Periodic Table All the elements in Group 1 of the periodic table form similar compounds. The metals lithium, sodium, and potassium all form compounds with a ratio of 2 atoms of the metal to 1 atom of oxygen. 13

14

15

GROUPS 1 & 2 VERY REACTIVE METALS Group 1 – The Alkali Metals The most reactive metals 1 electron in outer energy level Other shared properties – soft, silver colored; shiny; low density Group 2 – The Alkaline Earth Metals -very reactive, but less reactive than alkali metals 2 electrons in outer energy level Other shared properties – silver colored; more dense than alkali metals

THE TRANSITION METALS Groups 3-12 1 or 2 electrons in outer energy level Less reactive than alkaline earth metals Lanthanides and actinides are included in this group Other shared properties: shiny; good conductors of thermal energy and electric current; higher densities and melting points than elements in Groups 1 & 2

LANTHANIDES They follow the element Lanthanum. Shiny, reactive metals

ACTINIDES They follow the element Actinium All are radioactive. This means they are unstable. Elements listed after Plutonium (element 94) do not occur in nature. They are man made.

GROUP 13 Also known as the Boron Group 3 electrons in the outer energy level Group contains Boron (a metalloid) and 4 metals (Al - aluminum, Ga - gallium, In - indium & Tl- thallium) Reactive Other shared properties: solid at room temperature

GROUP 14 Also known as the Carbon Group 4 electrons in outer energy level Reactivity varies among the elements Group contains 1 nonmetal (carbon), 2 metalloids (Si - silicon & Ge - Germanium) and 3 metals (Sn - tin, Pb - lead and Uuq) Other shared properties: solid at room temperature

GROUP 15 Also known as the Nitrogen Group Have 5 electrons in the outer energy level Reactivity varies among the elements Group contains 2 nonmetals (N - nitrogen & P - phosphorus), 2 metalloids (As- Arsenic & Sb - antimony) & 1 metal (Bi - bismuth) Other shared properties: all but Nitrogen are solid at room temperature

GROUP 16 Also known as the Oxygen Group Have 6 electrons in the outer energy level Very reactive Contains 3 nonmetals (O - oxygen, S - sulfur & Se - selenium), 1 metalloid (Te - tellurium) & 2 metals (Po - polonium & Uuh) Other shared properties: all but Oxygen are solid at room temperature

GROUP 17 Also known as the Halogens Group contains all nonmetals (F - fluorine, Cl - chlorine, Br - bromine, I – iodine & At - astatine) Very reactive There are 7 electrons in the outer energy level Other shared properties: poor conductors of electric current; react violently with alkali metals to form salts; never found uncombined in nature.

GROUP 18 Also known as the Noble Gases Group contains all nonmetals (He - helium, Ne - neon, Ar - argon, Kr - krypton, Xe - xenon, Rn – radon & Uuo) There are 8 electrons in the outer energy level (He only has 2) They are unreactive. Other shared properties: colorless, odorless gases at room temperature

HYDROGEN Stands apart Only 1 electron in the outer energy level Very reactive Other properties: colorless, odorless gas at room temperature; low density; reacts explosively with oxygen.