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Chapter 4: Atomic Structure
4.1: Studying Atoms 4.2: The Structure of an Atom 4.3: Modern Atomic Theory
Ancient Greek Models of Atoms Democritus believed that all matter
consisted of extremely small particles that could not be divided.
Ancient Greek Models of Atoms
Democritus called these particles atoms from the Greek word atomos, which means “uncut” or “indivisible.”
He thought there were different types of atoms with specific sets of properties
Dalton’s Atomic Theory
Proposed the theory that all matter is made up of individual particles called atoms, which cannot be divided.
Compounds contain atoms of more than on element.
In a particular compound, atoms of different elements always combine in the same way.
Dalton’s Experiment
The ratio of the masses of the elements in the compound is always the same. A 100 gram sample of magnesium
combines with 65.8 grams of oxygen. A 10 gram sample of magnesium
combines with 6.58 grams of oxygen.
Thomson’s Experiment
Thomson’s experiments provided the first evidence that atoms are made of even smaller particles.
Thomson’s Model (plum pudding)
In an atom, the negative charges were evenly scattered throughout an atom filled with a positively charged mass of matter.
Rutherford’s Model All of an atom’s positive charge is
concentrated in its nucleus. The nucleus is a dense, positively charged
mass located in the center of the atom.
Pretending to be Alpha Particles Mv.
4.2:Structure of an Atom Protons, electrons, and neutrons are subatomic
particles. Because these particles are even smaller than an
atom, they are called subatomic particles. These three types of particles are arranged in an
atom as shown below.
What makes one element different from another if?
All protons are the same. All electrons are the same. All neutrons are the same.
Protons
The number of protons distinguishes an atom of one element from the atom of another element.
All atoms of the same element will have the same number of protons, and atoms of different elements will have different numbers of protons.
Properties of Subatomic Particles
Protons, electrons, and neutrons can be distinguished by mass, charge, and location in an atom.
Atomic Number The number of protons in an atom
of that element. Because the number of protons in an
atom remains the same during physical and chemical changes, we can refer to each element by the number of protons its atoms contain. This unique number is called the atomic number.
Atomic Number
Because atoms have an overall neutral charge, atoms have an equal number of protons & electrons.
# protons = # electrons
Isotopes atoms of the same element that have
different numbers of neutrons and different mass numbers.
Isotopes
1897: JJ Thomson Discovers the
electron He pictures
electrons embedded in a sphere of positive electric charge.
1911: Ernest Rutherford Atoms have a
dense, positively charged nucleus.
Electrons move randomly around nucleus.
Gold foil experiment