Unit 4: Atomic Structure (structure of the atom, electron configurations, Bohr atom)
Reading
BJU Chemistry: Ch. 4 "Atomic Structure"
AP: Zumdahl Chemistry Ch. 2 "Atoms, Molecules, and Ions" and Ch. 7 "Atomic Structure and Periodicity"
Topics
Labs
Virtual lab
BJU Chemistry: Ch. 4 "Atomic Structure"
AP: Zumdahl Chemistry Ch. 2 "Atoms, Molecules, and Ions" and Ch. 7 "Atomic Structure and Periodicity"
Topics
- Structure of the atom
- Electron energy levels
- Atomic number and atomic mass
- Isotopes
- Ions
Labs
- The "Oxygen gas lab" is our regular lab
Virtual lab
- Build an Atom weblab
All atoms are made from a nucleus of protons and neutrons, surrounded by a cloud of electrons. The quantities of protons, neutrons, and electrons are what distinguish one element from another.
Lecture outline:
The amazing history of the discovery of atomic structure
The amazing history of the discovery of atomic structure
- Dalton (1803) developed the first atomic theory of matter. Elements always combined in definite proportions to form compounds, therefore elements must exist as atoms or particles.
- J.J. Thomson (1890's) and the Plum Pudding Model. Electrons exist as discrete particles surrounded by a positively-charged substance, like plums in a plum-pudding. This was getting very close...
- Ernest Rutherford (c. 1900) discovered atoms are mostly empty space. Bombarded atoms with alpha particles and watched how they were deflected. Reasoned that the nucleus must be small, positively charged, and he named the positive particles "protons". This was called the Nuclear Model. This was a big leap forward.
- James Chadwick (1932) discovered the neutral particle in the nucleus, which was named the Neutron. He did this by bombarding metal with alpha particles. Rutherford had earlier 'suggested' that a neutral particle must exist, and Chadwick found it.
- Niels Bohr (1913) used the 'line spectra' of atoms to develop the first quantized atomic model. Scientists had wondered, 'why didn't the negative electrons spiral and crash into the positive nucleus?'... In the Bohr model, electrons orbited the nucleus in discrete energy levels, and thus did not crash into the positive nucleus. If an atom absorbed energy, the electrons would jump up to higher orbitals. If an electron jumped downward to a lower orbital, energy was given off in the form of light or heat. This was a huge development in thinking.
- Louise de Broglie (1920's) proposed that electrons exist as waves. Bohr's precise planet-like orbits were replaced by the wave functions of various shapes that we use today.
Electromagnetic Spectrum
An atom consists of a nucleus with protons and neutrons, surrounded by a cloud of electrons
- Visible light is a narrow band of the electromagnetic spectrum
- Shorter wavelengths of light (blue, violet) have more energy
- Longer wavelengths (orange, red) have less energy
- Spectroscopy is the analysis of light emitted or absorbed by things. When metals are heated, they produce distinct bright lines called line spectra, which led Niels Bohr to his quantum model of the atom.
An atom consists of a nucleus with protons and neutrons, surrounded by a cloud of electrons
- Protons have a charge of +1
- Neutrons have a charge of 0. They are neutral, in other words.
- Electrons have a charge of -1. Electrons are also really light. They're only 1/2000th the mass of a proton or neutron.
- Opposite charges attract. Like charges repel. This is called "electrostatics".
Electron energy levels
- Electrons don't circle around the nucleus like a planet going around the sun. Gravity has nothing to do with it.
- Electrons act like waves that fill energy levels
- The further out from the nucleus they are, the more energy they possess.
- Electrons are constantly jumping to higher levels, and then falling back to lower ones. When they jump to a higher one, they absorb energy; when they fall back down they give off energy.
- The following table gives the electron capacity of each energy level and sub-level.
The Aufbau Principle explains how electrons are added to an atom.
- Explains in what sequence the energy levels are filled.
- The gray arrows give the 'filling order' of energy levels within an atom
Atomic Number
Atomic Mass 'A' is the mass of one "mole" of an element
Isotopes have the same atomic number, but different numbers of neutrons, and thus slightly different masses. They chemically react the same, but can be separated using a centrifuge or other method.
Valence electrons are the outer electrons of an atom. These are the ones that take part in chemical reactions, and are thus the ones we really care about in chemistry.
- The atomic number 'Z' is the number of protons in the nucleus of an atom, and also the number of electrons in a neutral atom.
Atomic Mass 'A' is the mass of one "mole" of an element
- A mole is simply 6.02 x 10^23 particles of something. You have to specify if you are referring to atoms, or molecules, or jelly beans, or any other 'particle'.
Isotopes have the same atomic number, but different numbers of neutrons, and thus slightly different masses. They chemically react the same, but can be separated using a centrifuge or other method.
Valence electrons are the outer electrons of an atom. These are the ones that take part in chemical reactions, and are thus the ones we really care about in chemistry.
Oxygen lab
We will make and test oxygen gas. A classic lab exercise making and collecting an atmospheric gas, and testing it under different conditions.
We will make and test oxygen gas. A classic lab exercise making and collecting an atmospheric gas, and testing it under different conditions.
| o2_lab_handout.pdf |
Homework
| 3._atomic_structure_questions_2022.docx |
This video goes with the homework assignment above:
Biochemistry research assignment
Problem statement: The four most abundant elements by mass in the human body are oxygen, carbon, hydrogen, and nitrogen. These four elements make up about 96% of the human body. The next four most abundant elements are calcium, phosphorus, magnesium, and potassium.
Problem statement: The four most abundant elements by mass in the human body are oxygen, carbon, hydrogen, and nitrogen. These four elements make up about 96% of the human body. The next four most abundant elements are calcium, phosphorus, magnesium, and potassium.
- Write the ground-state electron configurations for these eight most abundant elements in the human body.
- Then choose any one of the eight; research and explain how the body obtains that element, and what function that element performs in the body (what does it do, chemically speaking?). Include pictures and diagrams, chemical equations, and any other information which helps explain its source & function in the body. This section should be 1-1/2 to 2 pages in length including diagrams.
Build-an-Atom weblab
| Build-an-atom_weblab_2022.doc |
Videos of standing waves
It's difficult to picture electrons as 'waves' which must occupy discrete 'orbitals' or energy-levels. If you think this is confusing, you're not alone!
The vibrating "Chlodni" plates (watch videos below) might help you visualize what standing waves look like - at least in 2 dimensions anyway. As the vibration frequency is increased in the videos (representing more and more energy input), the salt crystals arrange themselves at the wave "nodes". The steel plate vibrates as a wave, and the salt can only exist at the nodes, where there is no vibration.
In the same way, electrons can occupy only "discrete" orbitals - or energy levels - around an atom. They can't just sit anywhere they want; they must occupy discrete energy levels (orbitals or shells) which are numbered 1s, 2s, 2p, etc.
When you add energy (light of a certain wavelength, for example) to an atom, the electrons can jump up to a higher orbital. Conversely, when electrons jump down a level, light energy is emitted from the atom.
It's difficult to picture electrons as 'waves' which must occupy discrete 'orbitals' or energy-levels. If you think this is confusing, you're not alone!
The vibrating "Chlodni" plates (watch videos below) might help you visualize what standing waves look like - at least in 2 dimensions anyway. As the vibration frequency is increased in the videos (representing more and more energy input), the salt crystals arrange themselves at the wave "nodes". The steel plate vibrates as a wave, and the salt can only exist at the nodes, where there is no vibration.
In the same way, electrons can occupy only "discrete" orbitals - or energy levels - around an atom. They can't just sit anywhere they want; they must occupy discrete energy levels (orbitals or shells) which are numbered 1s, 2s, 2p, etc.
When you add energy (light of a certain wavelength, for example) to an atom, the electrons can jump up to a higher orbital. Conversely, when electrons jump down a level, light energy is emitted from the atom.