Atomic StructureAtomic Structure

HomeworkHomework

ObjectivesObjectives

• Be able to name and give the locations and charges of the three major subatomic particles.

• Explain what a chemical element is, and what determines an atom’s elemental identity.

• Be able to name and give the locations and charges of the three major subatomic particles.

• Explain what a chemical element is, and what determines an atom’s elemental identity.

AtomsAtoms

• What do you already know about atoms?– What IS an atom?– What are they made of?– What is their behavior?

• What do you already know about atoms?– What IS an atom?– What are they made of?– What is their behavior?

AtomsAtoms

• The atom is the basic unit of matter.– Anybody recall what matter is?

• The atom is the basic unit of matter.– Anybody recall what matter is?

AtomsAtoms• The atom is the basic unit of matter.

– Matter is anything that takes up space and has mass. So, the atom is the basic space-occupying unit.

– The physical and chemical properties of any substance depend upon what atoms it’s made of, and how they’re arranged.• Atom comes from the Greek “indivisible.” We now

know that there are things smaller than atoms, but atoms are the smallest things that still determine unique physical and chemical properties.

• The atom is the basic unit of matter.– Matter is anything that takes up space and

has mass. So, the atom is the basic space-occupying unit.

– The physical and chemical properties of any substance depend upon what atoms it’s made of, and how they’re arranged.• Atom comes from the Greek “indivisible.” We now

know that there are things smaller than atoms, but atoms are the smallest things that still determine unique physical and chemical properties.

AtomsAtoms

• A brief history to help illuminate the nature of an atom:– 6th century BCE, two Indian schools of

philosophy develop models of how tiny particles can be combined in pairs into more complex objects.

– Posited that there are four elements from which everything physical is made: earth, fire, air, water.

• A brief history to help illuminate the nature of an atom:– 6th century BCE, two Indian schools of

philosophy develop models of how tiny particles can be combined in pairs into more complex objects.

– Posited that there are four elements from which everything physical is made: earth, fire, air, water.

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AtomsAtoms

• Greek philosopher Democritus postulates that there exist atomos, uncuttable particles of matter between which there is only empty space, 450 BCE.

• Islamic scholars unite Greek and Indian ideas, and suggest that there are also particles smaller than atoms of which atoms could be themselves made up. This advance would later be lost, and the principle would have to be rediscovered.

• Greek philosopher Democritus postulates that there exist atomos, uncuttable particles of matter between which there is only empty space, 450 BCE.

• Islamic scholars unite Greek and Indian ideas, and suggest that there are also particles smaller than atoms of which atoms could be themselves made up. This advance would later be lost, and the principle would have to be rediscovered.

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AtomsAtoms

• Dark Ages of Europe, little progress in chemistry. Alchemists carry on some study but advances are limited by the magical/spiritual nature of their investigations.

• Chinese postulate existence of five elements, more as energies than as particles.

• Dark Ages of Europe, little progress in chemistry. Alchemists carry on some study but advances are limited by the magical/spiritual nature of their investigations.

• Chinese postulate existence of five elements, more as energies than as particles.

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AtomsAtoms• Robert Boyle (1661) argues for a return to atomic

theory rather than the Greek holdover of four primal elements.

• Antoine and Marie-Anne Lavoisier apply the term element to mean a basic substance that cannot be broken down or altered further.

• 1803-1805, John Dalton unifies the two proposals, suggesting that each element is really an atom of a particular type. Also, that compounds can only be formed by atoms combining in ratios of whole numbers: there’s no such thing as a half-atom.

• Robert Boyle (1661) argues for a return to atomic theory rather than the Greek holdover of four primal elements.

• Antoine and Marie-Anne Lavoisier apply the term element to mean a basic substance that cannot be broken down or altered further.

• 1803-1805, John Dalton unifies the two proposals, suggesting that each element is really an atom of a particular type. Also, that compounds can only be formed by atoms combining in ratios of whole numbers: there’s no such thing as a half-atom.

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AtomsAtoms• Dalton atom:

• Thomson (1903) posits from experimental data that atoms are made up of smaller particles, and that these particles have electrical charge: either positive or negative:

• Dalton atom:

• Thomson (1903) posits from experimental data that atoms are made up of smaller particles, and that these particles have electrical charge: either positive or negative:

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AtomsAtoms

• Rutherford (1911) experiments with passing particles of different charges through matter, finds results vary by charge. Posits that atoms are made of positively-charged particles in the center, and negatively-charged ones around them.

• Rutherford (1911) experiments with passing particles of different charges through matter, finds results vary by charge. Posits that atoms are made of positively-charged particles in the center, and negatively-charged ones around them.

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AtomsAtoms

• Bohr (1913) arrives at model of atom by studying emission spectra (we’ll study these later). Posits that the negative particles are “quantized,” they can only travel in circular orbits of certain sizes.

• Bohr (1913) arrives at model of atom by studying emission spectra (we’ll study these later). Posits that the negative particles are “quantized,” they can only travel in circular orbits of certain sizes.

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AtomsAtoms

• Today: Many important modifications to Bohr’s model, such as the varying shapes and energy levels of the orbitals, and quantum mechanics. – These things are way too weird for us to get

into here, though, and Bohr’s simpler model is still passable for explaining some broad trends in how atoms work.

• Today: Many important modifications to Bohr’s model, such as the varying shapes and energy levels of the orbitals, and quantum mechanics. – These things are way too weird for us to get

into here, though, and Bohr’s simpler model is still passable for explaining some broad trends in how atoms work.

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AtomsAtoms

• Atomic theory = matter is composed of atoms, and the properties of matter are determined by the structures and arrangements of the atoms involved.– Atomic theory is what’s called the “central

organizing theory” of chemistry, just as evolution is the central organizing theory of biology, and physics is hurting for its TOE uniting quantum and relativistic theory.

• Atomic theory = matter is composed of atoms, and the properties of matter are determined by the structures and arrangements of the atoms involved.– Atomic theory is what’s called the “central

organizing theory” of chemistry, just as evolution is the central organizing theory of biology, and physics is hurting for its TOE uniting quantum and relativistic theory.

Atomic StructureAtomic Structure

• The atom is generally delineated into two areas:– The nucleus is the small region at the

center of the atom.– We draw the nucleus pretty large in

diagrams so we can see the parts, but it’s really quite small. It’s anywhere from 1/23,000th to 1/145,000th the radius of the atom.

• The atom is generally delineated into two areas:– The nucleus is the small region at the

center of the atom.– We draw the nucleus pretty large in

diagrams so we can see the parts, but it’s really quite small. It’s anywhere from 1/23,000th to 1/145,000th the radius of the atom.

Atomic StructureAtomic Structure

• The nucleus is made of two kinds of subatomic particles:– Protons have a positive charge.– Neutrons have a neutral charge, i.e.

no charge.– Overall, does this mean that the

nucleus is positively charged, negatively charged, or not charged?

• The nucleus is made of two kinds of subatomic particles:– Protons have a positive charge.– Neutrons have a neutral charge, i.e.

no charge.– Overall, does this mean that the

nucleus is positively charged, negatively charged, or not charged?

Atomic StructureAtomic Structure

• In orbit around the nucleus are electrons, which are extremely tiny, and negatively charged.– Even though they’re small, they carry

just as much charge as a proton.

• In orbit around the nucleus are electrons, which are extremely tiny, and negatively charged.– Even though they’re small, they carry

just as much charge as a proton.

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Atomic StructureAtomic Structure

• Again!– What has a positive charge?– What has a negative charge?– What has a neutral charge?– Which one/s are in the nucleus?

• Again!– What has a positive charge?– What has a negative charge?– What has a neutral charge?– Which one/s are in the nucleus?

Atomic StructureAtomic Structure

• If all atoms are made up of the same three particles, and the same two are always only in the nucleus, how could we get different kinds of atoms?

• If all atoms are made up of the same three particles, and the same two are always only in the nucleus, how could we get different kinds of atoms?

Atomic StructureAtomic Structure• The periodic table is a table of the

chemical elements. It is in this shape for many very specific reasons.– Which of these variables determines what

element an atom is? Number of neutrons, number of electrons, number of available electrons, or number of protons?

• Just stick with the top three rows, Hydrogen through Argon.

• Write # of neutrons in yellow, # of electrons in blue, # of available electrons in purple, # of protons in red.

– Available electrons = electrons that can actually affect things.

• The periodic table is a table of the chemical elements. It is in this shape for many very specific reasons.– Which of these variables determines what

element an atom is? Number of neutrons, number of electrons, number of available electrons, or number of protons?

• Just stick with the top three rows, Hydrogen through Argon.

• Write # of neutrons in yellow, # of electrons in blue, # of available electrons in purple, # of protons in red.

– Available electrons = electrons that can actually affect things.

Atomic StructureAtomic Structure

• Each element has different physical and chemical properties, including what compounds it can form.

• An atom’s element depends upon how many protons the atom has.– All atoms with 2 protons are Helium. All

atoms with 79 protons are Gold. Etc.

• Each element has different physical and chemical properties, including what compounds it can form.

• An atom’s element depends upon how many protons the atom has.– All atoms with 2 protons are Helium. All

atoms with 79 protons are Gold. Etc.

Atomic StructureAtomic Structure

• Neutrons don’t affect bonds or properties, only mass.

• Why do you think it is that atoms almost always have just as many electrons as protons?

• Neutrons don’t affect bonds or properties, only mass.

• Why do you think it is that atoms almost always have just as many electrons as protons?

Atomic StructureAtomic Structure

– Electrons have a charge of -1, protons have a charge of +1. A proton attracts an electron.

– Protons determine the element and the number of electrons, and electrons will determine what compounds can form.• So, that is why different elements form

different compounds.

– Electrons have a charge of -1, protons have a charge of +1. A proton attracts an electron.

– Protons determine the element and the number of electrons, and electrons will determine what compounds can form.• So, that is why different elements form

different compounds.

Atomic StructureAtomic Structure

• Don’t throw those periodic tables away.• Let’s look some more at the layout of

the table and trends. (Book p. 142-143.)– Using the data from the periodic table, draw

a diagram of any three elements of your choice. (Don’t worry about electron orbitals for now, you can draw a Rutherford atom.)

– Label each one with its full name, its symbol, and its number of protons, neutrons, and electrons.

• Don’t throw those periodic tables away.• Let’s look some more at the layout of

the table and trends. (Book p. 142-143.)– Using the data from the periodic table, draw

a diagram of any three elements of your choice. (Don’t worry about electron orbitals for now, you can draw a Rutherford atom.)

– Label each one with its full name, its symbol, and its number of protons, neutrons, and electrons.