ATOMIC STRUCTUREDefining the Atom

OPENING What are we going to learn today?

Essential Questions: How did Democritus describe atoms? How did John Dalton further Democritus’s ideas on

atoms? What instruments are used to observe individual atoms?

GPS Standards: SCSh1b – Recognize that different explanations can be

given for the same information SCSh7c – Understand how major shifts in scientific

knowledge occur. SCSh7d – Hypotheses often cause scientists to develop

new experiments that produce additional data. SCSh7e – Testing, revising and occasionally rejecting new

and old theories never ends.

Why are we doing this? (logbook) What are some objects that require experimental

data in order to “picture” them, either because they are small or inaccessible?

Here’s how. (agenda) Discuss early models of the atom Begin gathering information for an atomic theory

timeline. Complete Section Review WS

Wrap-up Evaluate and criticize the following statements:

“All atoms are identical.” Chemical reactions occur when atoms of one element

change into atoms of another element.”

EARLY MODELS OF THE ATOM

atom Smallest particle of an element that retains its

identity in a chemical reaction Democritus (460BC – 370BC)

Greek philosopher One of the first to suggest the existence of atoms Believed that atoms were indivisible and

indestructible No attempt to explain chemical behavior No experimental support

John Dalton (1766 – 1844) English chemist and schoolteacher Dalton’s atomic theory

All elements are composed of tiny indivisible particles called atoms.

Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

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

Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Sizing up atoms Pure copper penny contains about 2.4x1022

atoms of copper 6x109 people on Earth

Radius of most atoms is between 5x10-

11m and 2x10-10m. Individual atoms can only be observed

by scanning tunneling electron microscope

SCANNING TUNNELING ELECTRON MICROSCOPE

SCE MICROSCOPE DEPICTION OF ELECTRON CLOUD

DIAGRAM OF SCANNING TUNNELING ELECTRON MICROSCOPE

QUANTUM FOREST

OPENING – 8/29/11 What are we going to learn today?

GPS Standards SCSh1b – Recognize that different explanations can be given

for the same information SCSh1c – Explain that further understanding of scientific

problems relies on the design and execution of new experiments which may reinforce or weaken opposing explanations.

SCSh7c – Understand how major shifts in scientific knowledge occur.

SCSh7d – Hypotheses often cause scientists to develop new experiments that produce additional data.

SCSh7e – Testing, revising and occasionally rejecting new and old theories never ends.

SC3a – Discriminate between the relative size, charge, and position of protons, neutrons, and electrons in the atom.

Why are we doing this? Essential Questions

What are 3 kinds of subatomic particles? How can you describe the structure of the

nuclear atom?

Here’s how. (agenda) Notes/discussion about the discovery of

protons, neutrons, and electrons Students work in pairs to complete a chart

about the three subatomic particles. Complete Section 4.2 Review Sheet

SUBATOMIC PARTICLES

Three kinds of subatomic particles Proton

Positive charge Neutron

No charge Electron

Negative charge

DISCOVERY OF THE ELECTRON

J.J. Thomson (1856 – 1940) Discovered the electron in 1897 Cathode ray tube experiments Hypothesized that cathode rays are tiny

negatively charged particles moving at high speed (electrons)

Measured the charge to mass ratio of the electron

Plum Pudding Model

Cathode ray deflected by a magnet

Plum Pudding Model

Robert Millikan (1868 – 1953) determined the quantity of charge on an

electron Used Thomson’s charge-mass ratio to

calculate the mass of the electron (1916) Oil drop experiments

MILLIKAN OIL DROP EXPERIMENT

DISCOVERY OF THE PROTON

Eugen Goldstein (1850 – 1930) Found rays traveling in the direction

opposite to that of the cathode rays in a cathode ray tube

Called these rays canal rays (later renamed protons)

DISCOVERY OF THE NEUTRON

James Chadwick (1891 – 1974) Discovered the neutron (1932)

PROPERTIES OF SUBATOMIC PARTICLES

Particle Symbol

Relative

Charge

Relative Mass(amu)

Actual Mass(g)

Electron e- 1- 1/18409.11x10-

28

Proton p+ 1+ 11.67x10-

24

Neutron n0 0 11.67x10-

24

DISCOVERY OF THE NUCLEUS

Ernest Rutherford (1871 – 1937) Gold foil experiments (1911) Findings

Atom is mostly empty space Small positively charged

nucleus Electrons move around

outside the nucleus Nuclear model

EXPLANATION OF RESULTS OF GOLD FOIL EXPERIMENT

Comparison of Thomson’s plum pudding model (top) and Rutherford’s nuclear model (bottom)

Notice that the nucleus in this model is solid. Protons and neutrons had not been discovered.

TICKET OUT THE DOOR

Write a paragraph explaining how Rutherford’s gold foil experiment yielded new evidence about atomic structure. Hint: First describe the setup of the experiment. The explain how Rutherford interpreted his experimental data.

OPENING Essential Questions:

What makes one element different from another? How do you find the number of neutrons in an atom? How do isotopes of an element differ? How do you calculate the atomic mass of an

element? Why is the periodic table useful?

GPS Standards: SC3c – Explain the relationship of the proton number

to the element’s identity. SC3d – Explain the relationship of isotopes to the

relative abundance of atoms of a particular element.

ATOMIC NUMBER

The number of protons in an atom identifies the element.

Atomic number the number of protons in the nucleus of an

atom Each element has a unique atomic number

Because atoms are neutral, the number of electrons(-1) must equal the number of protons(+1).

SAMPLE PROBLEM P. 111

How many protons and electron are in each of the following atoms? Fluorine Calcium Aluminum

MASS NUMBER

Mass number Total number of protons and neutrons in

the nucleus of the atom # neutrons = mass number – atomic

number

HYPHEN NOTATION

Name of element followed by a hyphen and the mass number

Examples Carbon – 12 Carbon – 14 Oxygen – 18

NUCLEAR NOTATION

The symbol of the element Mass number as a superscript before

the symbol Atomic number as a subscript before

the symbol

C126

ISOTOPES

Isotopes atoms of the same element that have

different masses Atoms that have the same number of

protons but different numbers of neutrons Atoms that have the same atomic number

but different mass numbers

Isotopes of hydrogen Protium

Hydrogen – 1 Deuterium

Hydrogen – 2 Tritium

Hydrogen – 3

ATOMIC MASS

Atomic mass unit (amu) 1/12 the mass of a carbon-12 atom Mass of a single proton or neutron is

approximately 1amu Atomic mass

weighted average mass (in amu) of the atoms in a naturally occurring sample of an element

Mass shown on the periodic table

CALCULATING ATOMIC MASS

Atomic mass = [(relative abundance)(atomic mass of the isotope)] for each naturally occurring isotope

Multiply the relative abundances (expressed as a decimal) times the mass of each isotope then add the results

SAMPLE PROBLEM, P. 117

Isotope Relative abundance

Relative abundance as decimal

Mass of isotope (amu)

Relative abundance

x mass (amu)

10X 19.91% 0.1991 10.012 1.99311X 80.09% 0.8009 11.009 8.817

Atomic mass = 1.993 amu + 8.817 amu = 10.81 amu

PERIODIC TABLE PREVIEW

Periodic table – an arrangement of elements in which the elements are separated into groups based on a set of repeating properties

Period Horizontal row on the Periodic Table 7 periods Properties vary as you move across a period

Group or family Vertical column of the Periodic Table 18 groups Elements within a group have similar properties