Chapter 4 Elements and the Periodic Table

Elements and the Periodic Table Background- – Matter – anything with mass and volume (“stuff”) There are basically 2 types of matter – Pure » Elements – the simplest form of matter, approximately 118 different elements » Compounds – combinations of 2 or more elements that are chemically combined to make a “new” substance – Mixed » Mixtures – combinations of 2 or more elements or compounds that are mixed together. No “new” substance » Solutions – liquid or gaseous mixtures

Elements and the Periodic Table Elements – the simplest form of matter – There are approximately 118 different elements – The smallest individual piece of an element is called an atom; so therefore there are approximately 118 different atoms

Elements and the Periodic Table – All atoms are composed of the same 3 particles put together in different ratios Neutrons– particles with no electrical charge Protons – particles with a positive electrical charge. The number of protons determines what the element is. Electrons – particles with a negative charge. In a “normal” atom the number of protons and electrons are always the same. – All atoms are spherical and can be separated into 2 areas The nucleus - The electron cloud

Elements and the Periodic Table The Nucleus – an internal spherical nugget that contains the protons and the neutrons. The nucleus comprises 99.99% of the atoms mass, but only about 1% of its volume. The Electron Cloud – makes up the outer layer of the atom, it contains rapidly moving electrons. The electron cloud comprises 0.01% of the atoms mass but 99% of its volume.

Elements and the Periodic Table The number of protons determines the properties of the element. On the periodic table the number of protons is called the Atomic Number (AN)

Elements and the Periodic Table The Periodic Table – All periodic tables are constructed the same way. Each box represents an element. Horizontal rows are called periods - The element boxes are arranged sequential left to right by the Atomic Number. Ex. 1,2,3,4,5,6,7, etc. Vertical columns are called families or groups – elements in a family all have similar properties, but are not sequencital. All periodic tables have a legend or key to explain the information in the boxes.

Elements and the Periodic Table The Periodic Table characteristics – Each box has the name of the element and its symbol. All symbols begin with a capital letter, if there is an addition letter it must be written as a lower case letter. – Each box has the atomic number and the atomic mass written someplace in them (see the key or legend for its location) The atomic number always represents the number of protons in the nucleus.

Elements and the Periodic Table Since the atomic number represents the number of protons and the number of protons is always the same as the number of electrons, we can find the number of electrons by knowing the atomic number.

Elements and the Periodic Table In addition, every Periodic Table has the elements Atomic Mass (aka Atomic weight). It is usually a number with a decimal in it. The Atomic Mass represents the average number of protons and neutrons in the nucleus of the element. To determine the number of neutrons in the most common atom of an element, you round this number off to the nearest whole number. This is called the Mass Number.

Elements and the Periodic Table The mass number is the exact number of protons and neutrons in the nucleus of the most common version of an elements atoms. protons To find the number of neutrons you subtract the number of protons from the mass number – Ex. AM = 132.7; MN = 133; # of protons = 57 therefore the # of neutrons = 76

Elements and the Periodic Table ABCD Name Symbol Atomic number # of Protons # of Electrons Atomic Mass Mass Number # of Neutrons

Elements and the Periodic Table More interesting facts from the Periodic Table – For ALL elements; The number of energy levels = the period number ie. Elements in the 3 rd period have 3 energy levels, elements in the 6 th period have 6 energy levels

Elements and the Periodic Table More interesting facts from the Periodic Table – Valence electrons are the electrons found in the outer most energy level. – We can determine the number of valence electrons for a select group of elements by looking at the “modified” family number of the elements found in the “towers”. The number of valence electrons = the family number – ie. Elements in the 4 th tower have 4 valence electrons; elements in the 7 th tower have 7 valence electrons

Elements and the Periodic Table Non-tower families (the transition metals) do not follow the rules for valence electrons. They have valence electrons, but we cannot determine them just by their family number or position on the periodic table.