9/18/ The Structure of an Atom THE STRUCTURE OF AN ATOM  VOCABULARY:  proton  electron  neutron  OBJECTIVES:  Identify three subatomic particles & compare their properties.  Distinguish the atomic number of an element from the mass number of an isotope, and use these numbers to describe the structure of an atom. VOCABULARY:  atomic number  mass number  isotope

9/18/ The Structure of an Atom 2 PROPERTIES OF SUBATOMIC PARTICLES  By 1920,  evidence for existence of 2 subatomic particles (+ & - charges)  Rutherford predicted existence of 3 rd particle  subatomic particles:

9/18/ The Structure of an Atom 3 COMPARING SUBATOMIC PARTICLES  distinguished by mass, charge, & location e - charge = in size to, but opposite of, charge of p +

9/18/ The Structure of an Atom 4 PROPERTIES OF SUBATOMIC PARTICLES: ELECTRONS  negatively (-) charged particles Thomson detected were later named electrons  Electron  symbol: e-  charge: negatively charged (1-)  location: in space outside of nucleus

9/18/ The Structure of an Atom 5  Rutherford also concluded that amount of positive (+) charge varies among elements  Proton  symbol: p +  charge: positively charged (1+)  location: in nucleus of atom PROPERTIES OF SUBATOMIC PARTICLES: PROTONS

9/18/ The Structure of an Atom 6 PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONS  Discovered in 1932, by English physicist James Chadwick  designed experiment to show that neutrons exist  concluded that particles he produced were neutral b/c a charged object did not deflect their paths

9/18/ The Structure of an Atom 7 PROPERTIES OF SUBATOMIC PARTICLES: NEUTRONS  Neutron  symbol: n  charge: neutral (0)  location: in nucleus of atom Hey Bartender! How much for a soda? For you… No charge.

9/18/ The Structure of an Atom 8 Proton: Neutron: Electron: Heavy, Positive Heavy, Neutral Light, Negative SUBATOMIC PARTICLES

9/18/ The Structure of an Atom 9 COMPARING SUBATOMIC PARTICLES

9/18/ The Structure of an Atom 10 COMPARING SUBATOMIC PARTICLES  everything known about nucleus & subatomic particles based on how particles behave  Currently, don ’ t have instrument to show inside of atom, but do have microscopes that show how atoms are arranged on a material ’ s surface (Page 111)

9/18/ The Structure of an Atom 11 ATOMIC NUMBER  Atomic number of an element equals the number of protons in an atom of that element.  i.e. 1 proton in nucleus of every hydrogen atom. Therefore, atomic number of hydrogen = 1.  Atoms of different elements have different number of protons.

9/18/ The Structure of an Atom 12 ATOMIC NUMBER  atoms are neutral  each + charge in an atom is balanced by a - charge.  Therefore atomic # of an element also equals # of electrons in an atom.  How many electrons does a hydrogen atom have?

9/18/ The Structure of an Atom 13 MASS NUMBER  Mass number - sum of the protons and neutrons in the nucleus of an atom.  i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number?

9/18/ The Structure of an Atom 14 MASS NUMBER  Mass number - sum of the protons and neutrons in the nucleus of an atom.  i.e. in an atom of aluminum there are 13 protons & 14 neutrons. What is the mass number? 13 protons + 14 neutrons = 27

9/18/ The Structure of an Atom 15 MASS NUMBER  try/animations/CHE1.3-an-animations.shtml try/animations/CHE1.3-an-animations.shtml

9/18/ The Structure of an Atom 16 MASS NUMBER  If you were given the mass number and atomic number of an atom, how can you find the number of neutrons?

9/18/ The Structure of an Atom 17 MASS NUMBER  If you were given the mass number and atomic number of an atom, how can you find the number of neutrons? Answer: by subtracting atomic # from mass # # of neutrons = mass # – atomic #

9/18/ The Structure of an Atom 18 ISOTOPES  Dalton ’ s atomic theory: all atoms of a given element are identical  Every atom of a given element DOES have same # of protons & electrons but does not have same # of neutrons.

9/18/ The Structure of an Atom 19 ISOTOPES  Isotopes - atoms of the same element that have different numbers of neutrons and different mass numbers.  Therefore, isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons. representation of two isotopes of carbon

9/18/ The Structure of an Atom 20 ISOTOPES  Hydrogen atoms:  all have 1 proton  most have no neutrons and mass # of 1 (hydrogen 1)  some have 1 neutron (hydrogen 2) or 2 neutrons (hydrogen 3)

9/18/ The Structure of an Atom 21 ISOTOPES  All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?

9/18/ The Structure of an Atom 22 ISOTOPES  All oxygen atoms have 8 protons. How many neutrons are in an atom of oxygen 18?  Answer: # of neutrons = mass # – atomic # mass # = 18 atomic # = 8 # of neutrons = 18 – 8 = 10

9/18/ The Structure of an Atom 23 ISOTOPES  hemistry/isotopes/ hemistry/isotopes/  hemistry/atoms/ hemistry/atoms/