Think of a gift you have received. Did you try to guess what was inside it without opening it? How did you figure it out?

Scanning Electron Microscope

Atomic Structure

4.1a Explain how Democritus and John Dalton described atoms. 4.1b Identify instruments used to observe individual atoms. 4.2a Identify three types of subatomic particles. 4.2b Describe the structure of atoms according to the Rutherford atomic model

An atom is the smallest part of an element that retains its identity in chemical reactions

Why do people use models? What models do you have or have you used? Early philosophers and scientists developed models of the atom to help explain the nature of matter

Greek Philosopher First proposed the idea of the “atom” No real evidence to support his claim

English Chemist and Schoolteacher Used scientific method to come up with Dalton’s Atomic Theory

1. All elements are made of tiny indivisible particles called atoms 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element

3. Atoms of different elements can physically mix together or can chemically combine in simple whole- number ratios to form compounds

4. Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination. Atoms of one element, however, are never changed to atoms of another element as a result of a reaction Atom AAtom B

ale/ ale/ Very small A copper coin contains 2 x atoms Most atomic radii are in the range of 5 x to 2 x meters

“All atoms are identical” FALSE- all atoms of a given element are identical “Chemical reactions occur when atoms of one element change into atoms of another element” FALSE- atoms of one element cannot change into another element

So, was Dalton correc t about atoms?

How can we see atoms? Electron microscopes use high speed electrons to see atoms

CarbonHydrogen

If we did the experiment that we did on Friday, but the marble passed under the table without being deflected most of the time, what might you conclude about the object underneath?

4.2a Identify three types of subatomic particles. 4.2b Describe the structure of atoms according to the Rutherford atomic model

Electrons are negatively charged subatomic particles. Discovered by English Physicist J.J. Thomson Cathode ray: a stream of electrons produced at the negative electrode (cathode) of a tube containing a gas at low pressure.

Measured the charge required to suspend an oil drop Determined mass of electron to be × grams

Protons are positively charged subatomic particles Much larger than electrons Discovered by Eugen Goldstein, when he saw that there existed another set of particles in a CRT traveling in the opposite direction

Neutrons are subatomic particles with no charge but have a mass nearly equal to that of a proton Discovered by James Chadwick

Ernest Rutherford and his colleagues performed the experiment

ord/ ord/

Where have you heard the term “Nucleus” before? The nucleus is the tiny central core in an atom and is composed of protons and neutrons

4.3a Explain what makes elements and isotopes different from each other and how isotopes of an element differ. 4.3b Calculate the atomic mass of an element.

Atomic number Atomic number is equal to the number of protons in an atom Unique to each element! Usually equal to number of electrons as well Mass number is the total number of protons and neutrons in an atom Mass number # of neutrons = mass number – atomic number

Mass number is in the superscript (on top) Atomic number is in the subscript (on bottom) How many neutrons does gold have? = 118 How many electrons does gold have? 79

Isotopes are atoms that have the same number of protons but different numbers of neutrons Neon-20 Neon-21 Neon-22 How many protons are in each? How many neutrons are in each?

Element Number of Protons Number of Electrons Number of Neutrons Atomic Number Mass Number Manganese25 30 Sodium 1112 Bromine35 45 Yttrium 3989 Arsenic Actinium 227

Element Number of Protons Number of Electrons Number of Neutrons Atomic Number Mass Number Manganese Sodium Bromine Yttrium Arsenic Actinium

Lesson Check 4.2 P. 122, question 51 Finish Lab Questions from Friday

In this class, I grade based on 50% Tests, 25% Labs, and 25% HW. If you received a 70 on tests, a 93 on HW, and an 85 on labs, what would your overall grade be?

4.3a Explain what makes elements and isotopes different from each other and how isotopes of an element differ. 4.3b Calculate the atomic mass of an element.

The mass of atoms are very small Instead of referring to their actual mass in grams, we use something more convenient Atomic Mass unit (amu)- one twelfth of a carbon atom Same as the mass of a proton or neutron

We use a mass number to refer to one individual atom. For an element with many atoms, we use atomic mass Weighted average mass of the atoms in a naturally occuring sample of the element

You have a sample of carbon that contains 98.89% carbon- 12 (12 amu), and 1.11% carbon-13 (13 amu). What is the atomic mass? Weighted average Atomic mass = (12.00 amu x ) + (13.00 amu x 0.011) = ( amu) + (0.144 amu) = amu

An element “X” has four major isotopes, which are listed below along with their abundances. Calculate the average atomic mass. What is the element? IsotopeMassPercent Abundance 46X X X X ?

Complete Vegium Lab Quiz tomorrow Test Friday