Organizing the Elements Chapter 4 Section 2

Mendeleev Russian scientist that discovered a set of patterns that applied to all the elements in 1869

Some elements have similar chemical and physical properties

Atomic mass is the average mass of all the isotopes of an element

He noticed that a pattern of properties appeared when he arranged the elements in order of increasing atomic mass

When Mendeleev arranged the 63 known elements by their atomic mass and arranged them into groups with similar properties, he had three blanks, which he correctly assumed were elements not discovered yet, and he even predicted some of their properties.

He published the first periodic table in 1869. A chart of elements showing the repeating pattern of their properties

Period is a row in the table

Family(group) is a column in the table

Table arranged by atomic number today

Organization of the Periodic Table The properties of an element can be predicted from its location of the periodic table. Arranged by increasing atomic number

Periods Horizontal rows (7) that contain a series of different elements

The properties of the elements change as you go from left to right (eg) elements on the left side are highly radioactive metals, less radioactive in the middle, and then the metalloids, followed by the nonmetals on the right.

The above pattern is repeated for each of the periods

Families 18 vertical columns

Consists of elements with similar chemical properties Note: the actinide and lanthanide series are not part of the families and periods

Reading an Element’s Square Each square includes the element’s atomic number, chemical symbol, name, and atomic mass

A symbol is a shorthand way to write the element’s name A symbol is a shorthand way to write the element’s name. It consists of a capital letter, a Capital letter and a lower case letter, or a Capital letter and two lower case letters

Elements names can be in any language, but most are either in Latin, English, or Russian

The atomic mass is an average because most elements have isotopes of varying atomic masses

How elements form in the sun The current theory is that all the elements discovered so far originally came from electrons that have escaped from stars.

Stars are made up of hydrogen, which is at high temperature and pressure. At this high temperature and pressure, Hydrogen exists as plasma ( a gas like mixture of free electrons and nuclei of atoms that have been stripped of electrons). Plasma has a positive charge, but the since the pressure and temperature is so great the particles do not repel each other.

Fusion When colliding nuclei have enough energy , they can join together.

Two small nuclei collide and fuse, forming a nucleus with a higher atomic number. Two larger nuclei then collide and fuse, forming a still larger nuclei and smaller nuclei which are released.