Chapter 4: The atom P 93 – 101 and

What is an atom?  Atoms: Makes up all matter Makes up all matter Are incredibly small Are incredibly small Determines the properties of matter Determines the properties of matter 91 different types of atoms 91 different types of atoms 20 synthetic atoms 20 synthetic atoms

The atomic theory  John Dalton devised a theory of the atom in 1808 Each element is composed of tiny indestructible particles called atoms Each element is composed of tiny indestructible particles called atoms All atoms of a given element have the same mass and properties that distinguishes them from other atoms/elements All atoms of a given element have the same mass and properties that distinguishes them from other atoms/elements Atoms combine in simple, whole number ratios to form compounds Atoms combine in simple, whole number ratios to form compounds

History of the atom  J.J Thompson (1856 – 1940) Discovered the electron Discovered the electron Negative chargeNegative charge Smaller and lighterSmaller and lighter Assumed to be a positive charge within the atom to balance electrons: plum pudding modelAssumed to be a positive charge within the atom to balance electrons: plum pudding model

History of the atom  Ernest Rutherford (1909) Gold foil experiment Gold foil experiment Alpha particles (+ charge) toward gold foil. Alpha particles (+ charge) toward gold foil. Alpha particles where deflected….there must be a large concentration of + charge Alpha particles where deflected….there must be a large concentration of + charge Came up with nuclear theory of the atom Came up with nuclear theory of the atom

History of the atom  Nuclear theory of the atom Most of the atoms mass and positive charge is in the nucleus Most of the atoms mass and positive charge is in the nucleus Most of the volume of the atom is empty space where tiny electrons sit Most of the volume of the atom is empty space where tiny electrons sit There are as many + charges as – charges so the atom is neutral There are as many + charges as – charges so the atom is neutral  Conclusions: The nucleus contains Protons (+) and neutrons (neutral) The nucleus makes up 99.9% of the mass of the atom The electrons are present in a cloud surrounding the nucleus

Atomic mass/atomic number  What are the 3 subatomic particles?  Which of the subatomic particles identifies an element? PROTONS! Each element has a different number of protons, thus making it unique. PROTONS! Each element has a different number of protons, thus making it unique.  Atomic Number: the # of protons in the nucleus of an atom  The # of protons is equal to the # of electrons. Why? Why?

Atomic Number

Problems:  How many protons are in Al?  How many protons are in V?  How many electrons are in Copper? 29 29

Mass Number  In an atom, where is most of the mass located? In the nucleus In the nucleus  What subatomic particles are in the nucleus? Protons & Neutrons Protons & Neutrons  Mass number is the mass found in the nucleus mass number: # of protons + # of neutrons  You can find mass number by looking at the shorthand notation.

Shorthand Notation  Used to show the mass # and atomic number of an element.  14 is the mass #  7 is the atomic #  N is the symbol for nitrogen

Shorthand Notation  Can also be written as: element-mass # Examples Nitrogen-14, Nitrogen-15, Nitrogen- 16 Examples Nitrogen-14, Nitrogen-15, Nitrogen- 16  How many neutrons are in each of the above elements?  What is the shorthand notation for gold-197?

Try These  What is the mass number of 40 Ca?  How many neutrons are in germanium-73?  How many protons, electrons & neutrons does zinc-65 have? Protons: 30 Protons: 30 Electrons: 30 Electrons: 30 Neutrons: 35 Neutrons: 35

Isotopes  Think about pizza…..  Isotopes are similar forms of the same element.  More specifically, isotopes have the same number of protons, but different number of neutrons.  If neutrons change, what else changes? Mass Mass

Atomic Mass  We must take in account all of the isotopes in order to get an accurate mass.  The mass on the PT is a weighted average of all the naturally occurring isotopes of an element.  This is called atomic mass.

Carbon Isotopes  Carbon has several isotopes  The two most naturally occurring isotopes are carbon-12 and carbon-13  This means C-12 and C-13 account for all of the atomic mass.  So how do we calculate atomic mass?

Carbon Isotopes  Carbon-12 Mass: amu Mass: amu (amu: atomic mass unit) (amu: atomic mass unit) Abundance: 98.89% Abundance: 98.89% How many neutrons are in carbon-12? How many neutrons are in carbon-12?  Carbon-13 Mass: amu Abundance: 1.11% How many neutrons are in carbon-13?

Carbon Isotopes  Atomic mass=(mass of isotope 1 x abundance) + (mass of isotope 2 x abundance) + (mass of isotope 3 x abundance)  ( x.9889) + ( x.0111)= amu  Find this value on your PT!

Hydrogen Isotopes  Hydrogen-1  Name: protium  Hydrogen-2  Name: deuterium 1e 1 p 0 n 1e 1 p 1 n

Hydrogen Isotopes  Hydrogen-3  Name: tritium 1e 1 p 2 n