Unit Topic: The Atom

Concept 1: Atomic Theory and Structure

Plum Pudding Model VS. Nuclear Model 

• Plum Pudding Model:

  • Has no nucleus, mass spread across the whole atom, solid with no empty space, and negative electrons are stuck or embedded inside the positive “pudding”.

• Nuclear Model:

  • Has a nucleus, mass concentrated to the nucleus, mostly empty space, positive charge is concentrated heavily into the nucleus, and negative electrons orbit the nucleus.

Bohr Model VS. Electron Cloud Model

• Bohr Model:

  • Circular, flat, and set paths of electrons, you can pinpoint the spot of an electron at any time, concentric 2D rings or shells.

• Electron Cloud Model:

  • Unpredictable, fuzzy cloud of probabilities, impossible to pinpoint exact position and momentum, 3D shapes like spheres, dumbbells, or lobes.

Electron Cloud

• The space surrounding the nucleus filled with electrons, which are in constant motion.

  • Where the volume of the atom is located

  • Negatively charged 

  • Broken down into regions of space called “shells” or “energy levels”

  • Electrons in different shells have varying energy levels

    • Shell closest to the nucleus has 2 electrons (least amount) and the lowest energy

    • Electrons in shells further from the nucleus have the most energy

Atom-Binding Forces

• Electromagnetic Force*:

  • The attractive force between the positive nucleus and the negative electron cloud is what holds the atom together

  • The repulsive force between negative electrons is what gives the electron cloud its volume

  • The repulsive force between positive protons gets overcome by strong nuclear force

• Strong Nuclear Force:

  • Quarks make up protons and neutrons

  • They have strong attraction which is what holds the nucleus together (despite the fact that protons repel each other)

*All electrically charged particles have this force of attraction (between opposite charges) and repulsion (between between similar charges).

Concept 2: The Periodic Table

Groups and Periods

• Groups (Vertical Columns):

  • Elements in the same group share highly similar chemical properties and reactivity because they have the same number of valence electrons.

• Periods (Horizontal Rows): 

  • Elements in the same period share the same number of electron shells, but their chemical properties change drastically from left to right as proton and electron counts increase.

• Elements in the same group often have similar properties because they have the same number of valence electrons. An example of this would be the alkali metals (group one), which have one valence electron, so they usually need to lose that one electron to become stable.

Metals, Nonmetals, and Metalloids

• Metals: 

  • Found on the left side and center of the periodic table. 

  • Solid at room temperature (with an exception of mercury, which is liquid)

  • Has luster (a shiny look) and great heat and electricity conductors

  • Both malleable and ductile (can be hammered thin or turned into wires)

• Nonmetals:

  • Found on the upper right side of the periodic table (hydrogen on the top left)

  • Can be solid, liquid, or gas a room temperature

  • Dull and non-reflective

  • Poor conductors, brittle as solids, and have low melting and boiling points

• Metalloids:

  • Found along the diagonal “stairstep” that separates metals from nonmetals

  • All are solid at room temperature

  • Can look shiny and metallic or dull

  • Semiconductors (can conduct at specific temperatures or conditions)

  • Brittle (just like nonmetals)

Hyphen and Nuclear Notation

Most common isotope of Hydrogen

• Hyphen Notation: 

  • Hydrogen-1

• Nuclear Notation:

  • ¹H

• The notation tells us the mass number of this particular hydrogen isotope

Electrically Neutral Atoms

• An atom is electrically neutral when it has the same number of protons and electrons (balancing the charges).

  • An atom not neutrally charged is called an ion

    • Cation: a positively charged ion, caused by the loss of electrons

    • Anion: a negatively charged ion, caused by the gain of electrons

Concept 3: Nuclear Chemistry

Nuclear vs. Chemical Reactions

• Nuclear Reaction:

  • Involves changes to the protons and neutrons inside the nucleus of the atom.

• Chemical Reaction:

  • Involves the breaking and forming of chemical bonds through the rearrangement of valence electrons outside the nucleus.

Alpha, Beta, and Gamma Radiation

Two Types of Nuclear Reactions

• Fission:

  • The splitting of one larger atom into two or more smaller ones.

    • Can happen spontaneously or when a neutron is fired into the nucleus, causing it to split.

    • Results in radioactive waste.

• Fusion:

  • The fixing/combining of 2 or more lighter atoms into one larger one.

    • Releases no radioactive waste.

    • Occurs in the stars.

    • Requires insane amounts of energy.

Nuclear Chemistry in the Real World

• Energy Through Nuclear Power Generation:

  • Uses controlled nuclear fission to generate heat, steam, and spin turbines for electricity.

    • Benefits: Produces tons of reliable, low-carbon energy without emitting fossil fuels.

    • Drawbacks: Generates long-lived radioactive waste that requires safe storage and carries the risk of accidents.

• Cancer Treatment:

  • Uses targeted radioisotopes to destroy malignant cancer cells.

    • Benefits: Damages or kills fast-growing cancer cells DNA.

    • Drawbacks: Can damage healthy surrounding cells, leading to hair loss or fatigue.

• Space Exploration: 

  • Uses heat from natural decay of radioactive isotopes to generate electricity for spacecraft.

    • Benefits: Provides continuous, maintenance-free power for deep-space probes journeying to distant planets.

    • Drawbacks: Involves high-risk launch materials and exposes equipment or people to high radiation challenges.