Activity 4: Are Atoms Divisible?

Ancient Greece Democritus Greek philosopher He thought atoms were uncuttable 3. Therefore: Atoms are indivisible particles Atomos—Greek meaning ‘indivisible 470-380 B.C.

John Dalton—late 18th century 1. What are atoms? 2. Do Carbon atoms differ from Oxygen atoms? Dalton’s Atomic Model: Hard, indivisible sphere 1766-1834 Yes

HAS THIS EVER HAPPENED TO YOU?

Are there things inside the atom? YES! Subatomic particles e- p+ n0

Discovery of electron (e-) Credited with the discovery of the electron in 1897. J.J. Thomson 1856-1940 Thomson identified a glowing beam of particles that traveled through a chamber of gas when exposed to an electrical current. Cathode ray tube

positive charges and repelled by negative charges. -This beam (cathode ray) was attracted to positive charges and repelled by negative charges. -Thomson concluded the beam must be composed of negatively charged particles. These came to be known as electrons.

Thomson’s Atomic Model “Plum Pudding” Model ELECTRONS EMBEDDED WITHIN POSITIVE CHARGE “If the atom contains negatively charged electrons, then there must also be something positively charged to keep the entire atom electrically neutral.” Negative electron plums are floating around in a sphere of positive pudding.

Discovery of the Nucleus 1871-1937 Ernest Rutherford

Rutherford’s Au foil Experiment “+” charge Rutherford’s experiment

Rutherford’s Nuclear Atom Negative electrons surround nucleus amidst lots of empty space. Positive Nucleus

Discovery of the proton Eugen Goldstein In 1886, Goldstein observed rays in a cathode ray tube that traveled oppositely than the electrons previously discovered.

Protons Located in nucleus Determine which element # of protons = atomic number equal to # of electrons in a neutral atom

Chadwick 1. 1932 discovered the neutron 2. This subatomic particle is heavy enough to split a nucleus 3. Led the way to the creation of the atomic bomb

LETS HAVE SOME PRACTICE Atomic Number (Protons) 6 C Carbon 12 Element Symbol Element Name Mass Number (Proton+Neutrons) Mass Number (Protons+Neutrons) C 12 6 Atomic Number (Protons) 20

Mass Number Almost all the mass of an atom comes from protons & neutrons # Protons + # Neutrons = mass number

LETS HAVE SOME PRACTICE Atomic # = # of protons # protons = # electrons in an atom Mass # = number of protons and neutrons So,to get the # of neutrons we must Subtract Atomic # from the Mass # = # Neutrons C 12 6 6 neutrons

Practice Determine the # of protons,neutrons, & electrons Protons B Mg 12 Zn Protons Neutrons Electrons He B Mg 12 Zn 30 35 Protons Neutrons Electrons He 2 B Mg Zn Protons Neutrons Electrons He B Mg Zn Protons Neutrons Electrons He B 5 6 Mg Zn

Subatomic Particles Electron: e- Proton: p+ Neutron: n or n0 negative charge 9.11 x 10-31 kg Proton: p+ positive charge 1.67 x 10-27 kg Neutron: n or n0 no charge

What did Battleship teach us? Battleship simulated Rutherford’s Gold Foil Experiment. Rutherford Battleship Alpha Particles Your missiles Nucleus Pattern Drawn Atom is mostly empty space All of the empty boxes

Anions= More Electrons Atoms vs Ions ATOMS IONS Protons = Electrons Protons ≠ Electrons Cations= More Protons Positive Charge Anions= More Electrons Negative Charge

IONS cation (+) anion (-) Li+1 Cl-1 3 Protons 2 Electrons 17 Protons

Ions An ion is a particle with a positive (+) or negative (-) charge Atoms that gain electrons have - charges Atoms that lose electrons have + charges

Isotopes Atoms of an element can have different numbers of neutrons – these are isotopes The number of protons and electrons is always the same, but since more neutrons add more mass, the mass number can be different

BUT……Neutrons are Different Isotopes Isotope Protons = Protons BUT……Neutrons are Different So Mass # is Different Atom Protons Neutrons Electrons Mass # Carbon-12 6 12 Carbon-13 7 13 Carbon-14 8 14

How Big Is An Atom?

Practice The atomic number of an atom is always equal to the total number of: a. Neutrons in the nucleus b. Protons in the nucleus c. Neutrons plus protons in the nucleus d. Protons plus electrons in the atom

Practice An atom of 42Ca contains: a. 20 protons and 22 neutrons b. 20 protons and 42 neutrons c. 20 electrons and 42 neutrons d. 20 electrons and 22 protons

Practice The nucleus of an Fe-56 atom contains: a. 26 protons, 30 neutrons and 26 electrons b. 26 protons, 26 neutrons and 30 electrons c. 26 protons and 56 neutrons d. 26 protons and 30 neutrons

Practice A 52Cr3+ ion contains: a. 24 protons, 52 neutrons, 21 electrons b. 24 protons, 28 neutrons, 24 electrons c. 24 protons, 28 neutrons, 27 electrons d. 24 protons, 28 neutrons, 21 electrons

Practice What is the total number of electrons in an atom with an atomic number of 30 and a mass number of 65? a. 30 b. 65 c. 35 d. 95