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Proton found in the nucleus of an atom; has a positive charge (+) Neutron found in the nucleus of an atom; has no charge (neutral) Electron found outside the nucleus of an atom; has a negative charge (-)

HELIUM ATOM + N N proton electron neutron Energy Level

A neutron is made of a proton and an electron. Thus, the net charge of a neutron is zero (a “+” and a “-” equals zero). Protons and neutrons have almost exactly the same mass (1 amu). Electrons have a mass that is about 1/1835 the mass of a proton. Therefore, we ignore it.

Representing Elements & Atoms He 2 4 Atomic mass Atomic number Elements are represented by symbols The superscript “4” in this case can be written on either side.

Atomic Number represents the number of protons for a particular element In neutral atoms, the number of electrons equals the number of protons Atomic Massrepresents the sum of protons and neutrons in a particular element NOTE: DO not confuse atomic # with atomic mass; Atomic mass is always the larger number.

Mg Atomic # Element Symbol Atomic Mass (this is an average mass) Elements are often represented in the following format in tables or charts

“Nuclear Symbols” He protons and 2 neutrons 2 protons In a neutral atom number of electrons = number of protons

Nuclear symbols are used by scientist as a standard way to represent elements, showing both the atomic and mass numbers mass number 1H11H1 atomic # 7 N Fe 56 Hydrogen has 1 proton, 0 neutrons, and 1 electron Nitrogen has 7 protons, 7 neutrons, and 7 electrons Iron has 26 protons, 30 neutrons, and 26 electrons

C Na H Se P = N = E = P = N = E = P = N = E = P = N = E = Find the # of protons, neutrons and electrons of each element

Practice Making Nuclear Symbols Atomic Number Symbol Name Atomic Mass 8 O 16 REMEMBER: In a neutral atom, the number of electrons = number of protons

Zn 65

Li 7

Si 28

B 11

Br 80

Matter consists of discrete, individual particles Elements are composed of indivisible particles called “atoms.” Used Cathode Ray Tubes (e.g. TV or computer monitor) to identify electrons Distinguished the nucleus (protons & neutrons) from electrons outside nucleus Developed the planetary model of the atom in which the electrons orbited around the nucleus A quick review of atomic model history

Bohr used the ROWS or PERIODS on the periodic table to represent the energy levels in an atom

Bohr Diagrams Find out which period (row) your element is in. Elements in the 1 st period have one energy level. Elements in the 2 nd period have two energy levels, and so on.

P = ? N = ? st 2nd 3rd 4th Each ROW or PERIOD has a particular number of electrons

Carbon is in period (row) 2

Practice Bohr Diagrams 6 p 6 n 6 p 6 n Draw a nucleus with the element symbol inside. Carbon is in the 2 nd period, so it has two energy levels, or shells.

Carbon Bohr Diagram Carbon has 6 electrons. The first shell can only hold 2 electrons. 6 p 6 n 6 p 6 n

Carbon Bohr Diagram Since you have 2 electrons already drawn, you need to add 4 more. These go in the 2 nd shell. 6 p 6 n 6 p 6 n

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne f)K 6 p 6 n 6 p 6 n

Bohr Diagrams Try the following elements on your own: a)H – 1 electron b)He c)O d)Al e)Ne f)K 1 p 0 n 1 p 0 n

Bohr Diagrams Try the following elements on your own: a)H b)He - 2 electrons c)O d)Al e)Ne f)K 2 p 2 n 2 p 2 n

Bohr Diagrams Try the following elements on your own: a)H b)He c)O - 8 electrons d)Al e)Ne f)K 8 p 8 n 8 p 8 n

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al - 13 electrons e)Ne f)K 13 p 14 n 13 p 14 n

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne - 10 electrons f)K 10 p 10 n 10 p 10 n

Bohr Diagrams Try the following elements on your own: a)H b)He c)O d)Al e)Ne f)K - 19 electrons Notice that the Electrons in the outermost energy level or shell were colored green … 19 p 20 n 19 p 20 n

2 e- p= 15 n= 16 2 e- 8 e-5 e- Another way to show the Bohr Model: Electrons in the outermost level are called valence electrons 15 P 31

Golden Rule of Atoms : All elements want to be happy! Or stable. One way to make an element “happy” (stable) is to fill its outer (valence) energy level. This usually happens when an atom has 8 valence electrons in its outermost energy level or shell. A good example is the neon atom. Ne

An element that loses electrons will develop a positive (+) charge like Na (sodium). A positive ion (cation) and negative ion (anion) will form an electrostatic attraction. Elements that gain or lose electrons to become happy or stable are called ions. An element that gains electrons will develop a negative (-) charge like Cl (chlorine).

Some elements are “happy” or stable on their own because they already have a complete valence or full outer energy level. These are the noble gases (in the rightmost column on the periodic table). All other elements will gain or lose valence electrons in order to have a full outer energy level.

The “Magic” number is 8

An element will gain or lose electron(s) in order to become stable. Will the elements below want to lose or gain electrons??????? Example: phosphorus Example: magnesium Phosphorus has 5 valence electrons & will gain 3 electrons in order to have a full valence level (8 electrons ) Magnesium has 2 valence electrons & will lose those 2 electrons in order to have a full valence level (2 nd level is full) Easier to gain 3 electrons than to lose 5 electrons Easier to lose 2 electrons than to gain 6 electrons

Notice how elements will lose or gain electrons to become stable (happy): SodiumSodium Na has 1 valence e- Na loses that e- to become Na+

ChlorineChlorine Cl has 7 valence e- Cl gains that e- to become Cl-

Opposites attract and they form an ionic bond.

Determine the # of protons, # of neutrons, and # of electrons Draw the atomic structure diagram for each atom MagnesiumOxygenPotassium P= N= E= P= N= E= P= N= E=