Comparison of Atomic Models

Learning Target Know the differences between electrons, protons, and neutrons. Determine the number of electrons and protons in a neutral atom and ion.

Relative Size

Electrons Charge: Negative (-) Mass: Near Zero Protons (positive) Charge: Positive (+) Mass: About 2000x Larger than electron Neutrons (neutral) Charge: Neutral Mass: Comparable to proton

A Little More About Charge A Coulomb (C) is an amount just like “a dozen” is an amount. 1C = 6.24x10 18 the charge of electrons The reason for this definition is because electrons are so small that we need to account for A LOT of them (10 18 ) to be able to describe a charge on the macroscopic scale.

Comparison of Subatomic Particles ParticleLocation Charge(C)Mass (g)Mass (amu) ProtonInside nucleus x x = 1 Neutron Inside nucleus 01.68x = 1 Electron Outside nucleus x x = 0

Atomic Number Given the symbol (Z) Represents the number of protons in an atom The atomic number also represents the number of electrons in a neutral atom of that element.

How many protons and electrons in the following atoms: 1. Na 2. Pb 3. Os

Ions (Atoms with charge) An atom that has either lost or gained one or more electrons. Gaining electrons means more negative than positive charges, so the ion is (-) Loosing electrons means more positive than negative charges, so the ion is (+)

How many protons and electrons does a magnesium atom have? What will the charge be if it loses 2 electrons? No. of protons: 12 (+) No. of electrons: 10 (-) Charge of Ion 2+ Write it like this: Mg 2+

Cu² + F Ion Protons Electrons Practice

YOU WILL NEED: –CALCULATOR –NOTEBOOK –PERIODIC TABLE

Learning Target Know how the atomic masses on the periodic table are calculated using the isotopes of the element. Know how to determine the number of protons, neutrons and electron in an atom or ion.

ParticleLocation Charge(C)Mass (g)Mass (amu) ProtonInside nucleus x x = 1 Neutron Inside nucleus x = 1 Electron Outside nucleus x x = 0

Atomic Mass Units (amu): roughly equal to the mass of a proton or neutron. **the mass of an atom is measured in amu’s 1 amu = 1.66x g Atomic Mass The mass of an atom is determined using the number of protons and neutrons in it. (electrons are ignored) Since the masses of atoms are so small in conventional mass units, like grams, we use a unit that is equivalent to the mass, in grams, of a proton.

Isotopes Isotopes are atoms that have the same number of protons but different numbers of neutrons In nature, elements are almost always found as a mixture of isotopes

Penny Isotopes Analogy the pennies are different atoms of the element penny (Pe).

Step #1 Mass of pennies 1. Record the total number of pennies in your container. 2. Separate your penny atoms into 2 categories: and earlier 2. Later than In 2 data tables (1 for pre-1982 and 1 for post-1982) record the year and mass of each individual penny. Some years may be duplicated – record each penny individually.

Step #2 Averages Calculate the average mass of the pennies in your sample that are 1982 or earlier. This is isotope #1 Calculate the average mass of the pennies in your sample that are post This is isotope #2

Step #3 Percentages Calculate the percentage of pennies that are pre1982 pennies in your container. Calculate the percentage of pennies that are post 1982 in your container. **KEEP THESE IN DECIMAL FORM. (0.47 not 47%)

Step #4 Calculate the Average Atomic Mass Use the formula: Average Atomic Mass = (decimal % of 1 st Isotope x Average Mass of 1 st Isotope) + (% of 2 nd Isotope x Average Mass of 2 nd Isotope) *Use decimal form of percentage in calculation..50 not 50%

Atomic mass Atomic Number/ number of protons Atomic mass: weighted average of the masses of the existing isotopes of an element.

HOW ARE PENNIES AN ANALOGY FOR ISOTOPES? What was Dalton’s 2 nd Postulate? (page 92) All atoms of a given element are identical, but they differ from those of any other element. Was it correct? Hmmm

Complete Chemical Symbols Mass number Atomic number Charge Ba 2+ Number of protons = Atomic # Number of neutrons = Mass # - Atomic # Charge = Atomic # – Number of electrons

Complete the Table Chemical Symbol No. of Protons No. of Electrons No. of Neutrons Atom or Ion? 38 Sr Atom 90

YOU WILL NEED: –CALCULATOR –NOTEBOOK –PERIODIC TABLE –3-3 Apply Worksheet

WARM UP What is the atomic mass unit of a proton? Neutron? Electron? What is the atomic mass of an element represent?

Practice What is the chemical symbol for the ion with 13 protons and 10 electrons? What is the chemical symbol for the ion with 7 protons and 10 electrons? How many protons and electrons are present in the S 2- ion? How many protons and electrons in Li + ion?

Mass Number – the sum of an isotope’s protons and neutrons. To name an isotope using chemical symbols, simply place the atom’s mass number to the upper left of the element symbol. For example 37 Cl.

Complete the Table Chemical Symbol No. of Protons No. of Electrons No. of Neutrons Atom or Ion? 38 Sr Atom 90