The table with a spot for everything The Periodic Table The table with a spot for everything

1800’s- only 63 known elements Many scientists look for patterns and similarities that will allow them to organize the elements

developed the first useful table of the elements Dmitri Mendeleev- Russian chemist developed the first useful table of the elements arranged elements in order of increasing atomic mass (average mass of all known isotopes) when he arranged the elements this way, he made several interesting observations: 1) The valence number (number of electrons in the outermost shell) of the elements occurred in a pattern of 1, 2, 3, 4, 3, 2, 1, etc.

2) When the elements were arranged in rows of 7, all of the elements in the resulting columns had similar chemical and physical properties 3) the properties of the elements in each row was periodic in nature Periodic- occurring in a regularly repeating pattern

As Mendeleev constructed his chart, every so often he would have to leave a blank space in order to make the known elements fit into columns with similar properties:

elements that had not been discovered yet he predicted that these empty spaces represented elements that had not been discovered yet (he was right) he also was able to accurately predict the properties of these missing elements

Modern Periodic Table Despite the importance of his work, Mendeleev’s table was not perfect… when the elements were arranged according to their atomic mass, several elements appeared to be misplaced in terms of their properties (for example: cobalt & nickel, copper & zinc, tellurium & iodine) therefore, 50 years after Mendeleev came the… Modern Periodic Table

Henry Moseley discovered the existence of neutrons was the first to determine the atomic number (number of protons) of elements when Moseley arranged the elements according to their atomic numbers instead of their atomic masses, it explained the “glitches” Mendeleev found

Moseley’s table is what is now known as the Modern Periodic Chart

Arrangement of the Periodic Chart

Rhodium Chemical Symbols a short-hand way of representing the elements - symbols can either have 1 or 2 letters, but never more than two! - the first letter is always a capital letter the second letter (if there is one) is always lower case Rhodium Example-

symbol- R Rh h ALWAYS lower case ALWAYS capitalized

Ca Fe the letters used to make up an element’s symbol can either come from the elements name in English or the element’s name in Latin examples- element- calcium Ca symbol- (from its English name) element- iron Fe symbol- (from the Latin Ferrum)

1.) columns of the table - called families - there are 18 families of elements

elements within the same family have similar but not identical properties for example- Family 1 (on the far left-hand side of the chart) includes lithium, sodium, potassium, rubidium, cesium, and francium - all are soft, shiny, silvery-white metals - all are highly reactive

But, of course, scientists don’t agree on what those groups should be… there are several groups of elements that may be made up of more than one family of elements But, of course, scientists don’t agree on what those groups should be… - some of the more common groups include: alkali metals boron group alkaline earth metals carbon group transition elements nitrogen group halogens oxygen group noble gases

2.) Rows of the Table - called periods elements in a period do not have similar properties as a matter of fact, the properties change a great deal as you go across a period however…

there is a pattern (that’s why they call it periodic): as you go from left to right, the first element is always going to be a highly reactive solid. the last element is going to be a a non-reactive gas

- there are seven periods of elements ?????? ?????? Hey, what up with those bottom two rows?

a section of periods 6 and 7 have been cut out and put below to make the chart easier to read cut

the rare earth elements - elements 57 – 71 are called the lanthanide series (because they come right after the element lanthanum) - elements 89 – 103 are called the actinide series (because they come right after the element actinium) - together, these two rows of elements are called the rare earth elements

using the periodic table - each element is found in a separate square - each element contains at least four facts: 1.) the element’s name 2.) the element’s symbol 3.) the element’s atomic number 4.) the element’s atomic mass

Types of Elements elements can be grouped into three main categories: 1.) metals 2.) nonmetals 3.) metalloids

Metals of the known elements, over 90 are metals

all but three (mercury, gallium, and cesium) are solids at room temperature

- good conductors of electricity and heat - usually have high melting points - usually shiny - are ductile (can be pulled into thin wires) - are malleable (can be hammered into thin sheets)

Nonmetals - of the known elements, 16 are nonmetals

at room temperature, 10 are gases, 5 are solids, and 1 (bromine) is a liquid are poor conductors of electricity and heat - have very low melting points - solids and liquids have dull surfaces - solids are brittle (break apart easily)

Metalloids found along the dividing line between the metals and nonmetals

- all are solids at room temperature have properties of both metals and nonmetals includes: boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine

Periodic Properties of the Elements

you know that some properties of elements vary in a regular way as you go from left to right across a period, but which ones? - there are 4: 1.) electron arrangement 2.) reactivity 3.) atomic size 4.) metallic properties

1. electron arrangement the valence number of an element refers to the number of electrons in the outermost shell

- only the valence electrons are involved in bonding - valence electrons can be gained, lost, or shared - elements on the left side tend to lose electrons easier - elements on the right tend to gain electrons easier

for example: Lithium Oxygen found on left side of chart found on right side of chart - has 1 valence electron - has 6 valence electrons - tends to lose electrons easily - tends to gain electrons easily

2. reactivity - the ability of an element to bond with other elements - elements on the left side tend to react a lot with other elements - elements on the right side do not react at all

3. atomic size - within a period, atoms get smaller as you go from left to right why? because as you add electrons to a shell, there is more magnetic attraction between the electrons and the protons

4. metallic properties (oh, you remember… good conductor, high melting point, shiny, ductile, malleable, etc…) - as you go from left to right, the elements become less metallic in nature