Antoine Lavoisier In the late 1790s, he compiled a list of the known elements at the time. This list contained 23 elements.
But times were about to change… In the 1800’s, there were many changes in the world - Electricity
- Spectrometer
- Industrial Revolution
As a result, there was an increase in the number of known elements - By the 1870, there were 70 known elements
An agreement is reached… Then in the 1860’s, chemist agreed upon a method for accurately determining the atomic mass of elements.
John Newlands Noticed when elements were arranged by atomic mass, they repeated properties every 8th element. He used the word periodic to describe this pattern
Unfortunately… Did not work for all the elements Criticized because of its association with music Did give others the idea of repeating properties - periodic
Lothar Meyer and Dmitri Mendeleev Each made a connection between atomic mass and properties of elements
The winner is… In addition, Mendeleev predicted unknown elements However, not completely correct – new elements weren’t in correct order What do you notice about elements 27 & 28 and 52 & 53?
Henry Moseley Solved this problem by arranging the elements by increasing atomic number. The periodic repetition of chemical and physical properties of elements when arranged by atomic number is now known as Periodic Law
Remember Atomic number = the number of protons = the number of electrons (if neutral) Atomic Mass on the Periodic table is the average mass of the isotopes - But the mass number of each isotope is the protons plus the neutrons
Chemical Symbol The symbol that refers to the element First letter is capitalized, second letter (if applicable) is lower case Not all symbols are based on English names for the elements, some come from their Latin names or even other languages
Columns and Rows The columns are called Families or Groups - Earlier Version had 1-8 followed by A or B
- Group A elements are called Representative Elements
- Group B elements are called Transition Elements
- Modern Version labels the columns with 1-18
Rows are called Periods - Seven periods for the seven energy levels (rings)
Classifying Elements Three Types of Elements - Metals
- Nonmetals
- Metalloids
Metals Solid at room temperature Good conductors of heat and electricity Most are ductile and malleable
Nonmetals Upper Right side of the Periodic Table Generally brittle solids or gases Poor conductors of heat and electricity
Metalloids A.k.a – the semi-metals Boxes bordering the stair-step Physical and chemical characteristics of both metals and nonmetals
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