Chapter 5 Atomic Structure & the Periodic Table

Element Names and Symbols Each element has its own unique symbol For some its simply the 1 st letter of its name Ex. H- Hydrogen Others use the 1 st letter plus one other letter of the elements name Ex. Ca- Calcium The 1 st letter is always capitalized and the 2 nd lower case

Element Names and Symbols Some symbols come from the elements Latin name Ex. Gold- Au- aurum

Structure of an Atom Atoms are made of three types of particles 1. Protons- positively charged particles 2.Neutrons- uncharged particles 3.Electrons- negatively charged particles The combination of protons and neutrons make up the nucleus of the atom

Atomic Number The identity of an atom is determined by the number of protons in its nucleus

Atomic Mass Number Is the total amount of protons and neutrons in an atoms nucleus Atoms always have the same number of protons but may not always have the same number of neutrons

Atomic Mass Number Isotopes are atoms of the same element that have a different number of neutrons A particular isotope is designated by the name of the element and the total number of protons and neutrons

Ions Each atom has an electron 1 (-) charge and each proton has 1 (+) charge B/c the charges are balanced the atom has no overall electrical charge An ion is formed when an atom loses or gains one or more electrons If an atom loses one electron the charges are no longer balanced. There is one more proton than electrons therefore the atoms has a positive charge Ex/ Na +, Ca 2+, Al 3+

Ions When a (-) ion is formed an electron is added and it increases the repulsion causing the ion to expand

Element organization Separating elements by the masses of their atoms is a way of organizing the elements The atomic mass of the atoms of an element is the average mass of all the elements isotopes The 1 st periodic table was organized based on physical and chemical properties and was produced by Mendeleev in 1869

Element Organization The periodic table shows a periodic or repeating pattern of properties of the elements Periodic tables now differ from Mendelev’s table in many ways 1.Elements with similar properties are found in columns not rows 2.Elements are not arranged by atomic mass but by atomic number

Groups and Periods Elements in a vertical column of the periodic table show similarities in their chemical and physical properties Elements in a column are known as a group and are labeled by a the top of the column Each horizontal row in the periodic table is called a period Properties of elements change from one end of a period to the other

Groups and Periods An elements position in the table can give info about the element Atoms on the left side of the table form (+) ions Group 1 atoms form ions w/one (+) charge(1+) Group 2 lose two electrons to form ions w/a charge of (2 + ) Group 18 doesn’t form ions Group 17 atoms gain one electron forming a (-) ion 9(1-)

Groups and Periods Group 16 atoms gain 2 electrons to form a (2-) ion Group 3-12 form (+) ions but charges vary Sizes of atoms vary across periods & w/in groups Densities generally increase from the top of a group to the bottom

Regions of a Periodic Table An elements position on the table also indicates how reactive it is Reactive meaning how likely an element is to undergo a chemical change Elements in group 1& 17 are the most reactive Group 18 elements are the least reactive

Metals Most of the elements are metals on the periodic table Most metals conduct electricity, heat well, have a shiny appearance and can be easily shaped by pounding, bending, or being drawn into a long wire

Reactive Metals The alkali metals (group 1) are very reactive w/ oxygen and water vapor Alkaline earth metals are less reactive

Transition Metals Group 13-2 Copper, gold, silver and iron are some of the earliest known metals They have been used to make jewelry and coins

Rare Earth Metals Located in the top row of the two rows of metals that are usually shown outside the main body of the periodic table They are called rare b/c it was once thought that these elements were available only in tiny amounts in the Earth’s crust As mining improved it was found that they were hard to isolate in pure forms

Non Metals Elements on the right side of the periodic table are non metals Properties tend to vary from one element to the next Solid non metals often have dull surfaces, cannot be shaped by hammering or drawing into wires, are poor conductors of heat and electric current

Halogens Group 17 elements Greek words mean “forming salt” Very reactive, easily form compounds called salts w/many metals b/c they are so reactive halogens are often used to kill microorganisms

Noble Gases Group 18 elements Called noble or inert b/c they almost never react w/ other elements

Metalloids Are elements that have properties of both metals and non metals Metalloids often make up the semiconductors found in electronic devices

Radioactivity In the early 1900’s Marie Curie named the process by which atoms produce energy particles and radioactivity Curie was the 1 st person to isolate polonium and radium which are two radioactive elements An isotope is radioactive if the nucleus has too many of too few neutrons

Radioactive Decay Radioactive decay occurs at a steady rate that is characteristic of the particular isotope The amount of time that it takes for ½ of the atoms in a particular sample to decay is called the half life of the isotope The ½ life is a characteristic of each isotope and is independent of the amount of material