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The Structure of the AtomChapter 4.2
Bell Ringer1. The ancient Greek philosopher Democritus coined what word for a tiny piece of
matter that cannot be divided?a) Elementb) Electronc) Atomd) Molecule
2. Dalton’s theory (~1800; based on behavior of gasses) included all but one of the following points. Which is not from Dalton?
a) All elements are composed of atoms.b) Most of an atom’s mass is in its nucleus.c) Compounds contain atoms of more than one element.d) In a specific compound, atoms of different elements always combine in the same
way.3. J. J. Thomson’s gas tube electrical experiments (~1897) provided first evidence of:
a) Atomsb) Nucleusc) Subatomic particlesd) Elements
4. Rutherford’s gold foil experiment (~1914) provided evidence for one of these:a) Negative and positive charges are spread evenly throughout an atom.b) Alpha particles have a positive charge.c) Gold is not as dense as previously thought.d) There is a dense, positively charged mass in the center of an atom.
Properties of Subatomic Particles
J.J. Thomson was the first to detect subatomic particles
Electron: ______________charged subatomic particle.
› Found in the space outside the nucleus.› Very light mass –
› Charge of 1-.
Thomson’s ExperimentsIn his experiments, J. J. Thomson used a sealed tube containing a very small amount of gas.
Thomson’s Model of the Atom
Metal disk
Metal disk
Metal disk Source of electric current
Properties of Subatomic Particles
Rutherford found positive charge varies among the elements. › Based on experiments with gold and
other elements.
Proton: ___________charged subatomic particle
› Found in the nucleus of an atom. › Charge of 1+. › Each nucleus contains at least one
____________
The Gold Foil Experiment
Rutherford’s Atomic Theory
Source of alpha particles
Slit
Screen
Gold atoms
Alpha particles
Nucleus
Properties of Subatomic Particles
James Chadwick 1932 - the English physicist carried out an experiment to show that _____________exist.› Radioactive decay produced particles about
the mass of a _________but without any charge.
› Proved the particles produced were neutral because a charged object did not __________ their paths.
3) Neutron: › Neutral (no charge) subatomic particle › Found in the nucleus of an atom.› Mass ~
Everything we know about subatomic particles is based on how the particles behave in experiments.
› Scientists still do not have an instrument that can show the inside of an atom.
Comparing Subatomic Particles
Comparing Subatomic Particles
Mass• Protons and neutrons have almost the same
mass.Mass of ~__________________= the mass of
one proton.
Charge• An electron charge (-1) is _________in size but
the ________________sign of a proton charge (+1).
• Neutrons have no charge.
Location in the atom • Nucleus -• Outside the nucleus -
Subatomic Particles - Protons
Atoms of different elements have different numbers of ____________.
Atomic Number =
For any given element: All atoms have same atomic _____________.
› Hydrogen has 1 proton; atomic number =› Helium has 2 two protons; atomic number =› Etc.
Each element has a ________atomic number.
Atomic Number and Mass NumberEach element has a different atomic number.
›A The atomic number of sulfur (S) is›B The atomic number of iron (Fe) is ›C The atomic number of silver (Ag) is
Atomic Number and Mass Number Atoms are neutral when:
• Each positive charge in an atom is ______________ by a negative charge. i.e. # of ____________= # of _____________ Each proton has an electron to offset its charge
Examples:• Hydrogen atomic number = 1
Each neutral hydrogen atom has 1 proton & 1 electron.
• Sulfur atomic number = 16 Each neutral sulfur atom has 16 protons & 16
electrons.
Atomic Number and Mass Number Mass Number = _________ of protons +
neutrons. To find # of neutrons (when mass # &
atomic # are known): # of neutrons =
Example: Aluminum with mass # = 27 Mass # = 27 Atomic # = 13. 27 - 13 protons = 14 neutrons
Atomic Number and Mass Number
Charged Atoms
An atom becomes charged when it __________ or _________ an electron (e-).› Positive Charge = _________ of e-’s
H becomes H+1
› Negative Charge = ___________ of e-’s H becomes H-1
Electrons are the only subatomic particle that can be gained or lost.
Isotopes Isotopes = same element; different #
_________
Isotopes of an element:1)Same # of protons
• i.e. same __________ number
2)Different # of neutrons• Different atomic _________ because of
the neutrons
Isotopes Isotopes are referred to by ______
number› For example, oxygen has 3 isotopes:
“oxygen ___”, “oxygen ___”, and “oxygen ___”
All three oxygen isotopes have same reactions
› Examples: All combine with hydrogen to form
water All combine with iron to form rust.
Isotopes
Most elements: Physical and chemical properties of ___________ are very similar.
Hydrogen is an ____________. ›Hydrogen-1 no neutrons (most H is hydrogen-1) ›Hydrogen-2 has one neutron›Hydrogen-3 has two neutrons.
Because a hydrogen-1 atom has only one proton, adding a neutron ___________its mass.
Heavy Water - hydrogen-2 atoms & oxygen-16
Hydrogen-2 atoms twice the mass of Hydrogen-1› Properties of heavy water are different from the
properties of ordinary water.
Isotopes
Assessment Questions
1) Of the subatomic particles that form the atom, the one with the smallest mass is:
a) Neutron. b) Electronc) Protond) Nucleus
Assessment Questions
2) Of the subatomic particles that form the atom, the one with the positive charge is:
a) Neutron. b) Electronc) Protond) Nucleus
Assessment Questions
3) Of the subatomic particles that form the atom, the one with the neutral charge is:
a) Neutron. b) Electronc) Protond) Nucleus
Assessment Questions
4) Of the subatomic particles that form the atom, which ones are found in the nucleus?
a) Neutron. b) Electronc) Protond) None
Assessment Questions
5) In which way do isotopes of an element differ? a. number of electrons in the atomb. number of protons in the atomc. number of neutrons in the atomd.net charge of the atom