Chapter 2 pt.1

Water: $H_2O$ (two hydrogen atoms and one oxygen atom).
Hydrogen Peroxide: $H2O2$ (two hydrogen atoms and two oxygen atoms).
Copper Chloride Compounds:
- One type has a 1:1 ratio of chlorine to copper.
- Another type has a 2:1 ratio of chlorine to copper, demonstrating whole number ratios in chemical formulas.

Components of the atom have charges.
Proton:
- Has a positive charge.
- Mass of approximately one atomic mass unit (1 u).
Neutron:
- Neutral (uncharged).
- Mass of approximately one atomic mass unit (1 u).
Electron:
- Has a negative charge.
- Much smaller mass compared to protons and neutrons.

High voltage applied to a cathode and anode.
Cathode ray produced.
Using magnets and charged plates, the cathode rays (later identified as electrons) were observed to be deflected.
Negatively charged particles are repelled by negative fields and attracted to positive fields.

Fine mist of oil droplets sprayed.
X-rays used to produce charges on the oil droplets.
By adjusting the charge, droplets could be suspended.
Observations allowed for the determination of the charge and mass of the electron.
The charge on the droplets was always a multiple of $1.6 \times 10^{-19}$ coulombs.

Alpha particles (positively charged) were directed at a thin gold foil.
Observations:
- Most particles passed straight through.
- Some particles were slightly deflected.
- A very small number of particles were significantly deflected or bounced back.
Conclusions:
- Atoms are mostly empty space.
- The nucleus is very small and dense, containing most of the atom's mass and positive charge.
- The diameter of a nucleus is about $10^{-15}$ meters, while the atom's diameter is about $10^{-10}$ meters.
- The nucleus is about 100,000 times smaller than the atom.

Soccer Stadium Analogy: If a soccer stadium represents an atom, a proton is like a tennis ball in the center, and an electron is like the head of a pin.
Basketball Analogy: Placing a basketball in the middle of a stadium to represent the nucleus and its size relative to the atom.
Electrons distributed throughout the empty space of the atom.
Alpha particles are much more massive than electrons, so electrons don't significantly affect the path of alpha particles.

All atoms of an element have the same number of protons.
The number of protons determines the type of element.
In a neutral atom, the number of electrons equals the number of protons.
Isotopes: Atoms of the same element with different numbers of neutrons, leading to different masses.

Atomic Number (Z): Number of protons (written as a subscript at the bottom left of the element symbol).
Mass Number (A): Total number of protons and neutrons (written as a superscript at the top left of the element symbol).
Number of neutrons = Mass Number - Atomic Number (A - Z).

Carbon-12: Carbon with a mass number of 12. Denoted as $^{12}_6C$ . Contains 6 protons and 6 neutrons.
Carbon-14: Radioactive isotope used for carbon dating. Contains 6 protons and 8 neutrons.
Neptunium-237: Denoted as $^{237}_{93}Np$ . Contains 93 protons and 144 neutrons.

To find the number of neutrons, subtract the atomic number (number of protons) from the mass number.

The number at the bottom of an element's symbol on the periodic table is the average atomic weight.
It's a weighted average of the masses of all the isotopes of that element.

Early in the periodic table, the number of neutrons and protons are nearly equal.
As you move past calcium (Ca), more neutrons are needed to stabilize the nucleus.
Neutrons help counteract the repulsion between protons in the nucleus.
Elements with a large number of protons (e.g., Neptunium) tend to be unstable and undergo radioactive decay.
Elements past bismuth (Bi) are generally radioactive.

Charge is indicated as a superscript to the right of the element symbol.
The charge represents the difference between the number of protons and electrons.
Positive Charge: Indicates more protons than electrons.
Negative Charge: Indicates more electrons than protons.
- Example: Chlorine, $Cl$ , element 17, usually has a charge of $-1$ . Chlorine with one more electron 17 protons and 18 electrons leads to the ion, $Cl^{-}$
Example: $He^{2+}$ (Helium with 2 protons and no electrons).
Example: $Mg^{2+}$ (Magnesium with 12 protons and 10 electrons).

Atomic mass is the mass of an atom.
Average atomic mass (or atomic weight) is the weighted average of the masses of the isotopes of an element.
$1 \text{ gram} = 6.02214 \times 10^{23} \text{ u}$
Avogadro's number of atomic mass units is equal to one gram.

The average atomic mass is calculated using the masses of the isotopes and their relative abundances.
Formula: Average atomic mass = $\sum (mi \times pi)$ , where $mi$ is the mass of isotope i and $pi$ is the fractional abundance of isotope i.

Carbon-12: 98.892% abundance, mass = 12 u (exactly).
Carbon-13: 1.108% abundance, mass = 13.00335 u.
Average atomic mass of carbon = $(0.98892 \times 12) + (0.01108 \times 13.00335) = 12.011 \text{ u}$

Hydrogen: 99.99% hydrogen-1, 0.01% hydrogen-2 (deuterium).
Carbon: Approximately 99% carbon-12, 1% carbon-13.
Nitrogen: Over 99% nitrogen-14, with a small amount of nitrogen-15.
Oxygen: Predominantly oxygen-16, with smaller amounts of oxygen-17 and oxygen-18.
Chlorine: Has two main isotopes, chlorine-35 and chlorine-37; chlorine is mostly chlorine-35.

Copper-63: 69.17% abundance, mass = 62.9296 u
Copper-65: 30.83% abundance, mass = 64.9278 u
Average atomic mass of copper = $(0.6917 \times 62.9296) + (0.3083 \times 64.9278) = 63.5456 \text{ u}$