Atoms and Elements Notes

Atoms are the fundamental particles that constitute everything in the universe, including stars, rocks, water, T-shirts, butterflies, and living beings.
Atoms are incredibly small and cannot be observed using conventional microscopes; they require a powerful scanning tunneling microscope (STM) for visualization.

Atoms are composed of three primary particles:
- Protons: Positively charged particles located in the nucleus.
- Neutrons: Electrically neutral particles also located in the nucleus.
- Electrons: Negatively charged particles orbiting the nucleus in electron shells.
The nucleus, situated at the center of the atom, is a dense cluster of protons and neutrons.
Electron shells are the outermost regions of the atom where electrons reside.

The nucleus is a compact and dense assembly of protons and neutrons at the atom's center.
Neutrons have a slightly greater mass than protons, but both are approximately 1800 times heavier than electrons.
Consequently, the majority of an atom's mass is concentrated in its nucleus.
Protons possess a positive electrical charge (+), while neutrons are electrically neutral (no charge).
The collective positive charge of the protons imparts a positive charge to the entire nucleus.

Electrons revolve around the nucleus in the space surrounding it.
Electrons carry a negative charge (–) and are drawn to the positively charged nucleus.
This attraction prevents electrons from drifting too far from the nucleus but doesn't pull them into it completely.
Atoms are electrically neutral, meaning the quantity of electrons is consistently equal to the quantity of protons.
- $Number \space of \space electrons \space in \space an \space atom = number \space of \space protons$

Electrons orbit the nucleus within specific regions known as electron shells or energy levels, rather than spinning randomly.
The innermost electron shell, closest to the nucleus, experiences the strongest attraction to the nucleus.
- This shell represents the lowest energy level for electrons.
Electrons in the outermost shell possess the highest energy.
The first electron shell, being relatively small, can accommodate a maximum of two electrons.
The subsequent electron shell, situated slightly farther out, is larger and can hold up to eight electrons.
The capacity of an electron shell to hold electrons increases with distance from the nucleus.
The maximum number of electrons that a shell can hold is determined by the formula: $2n^2$ , where n represents the shell number.
- Shells and Maximum Number of Electrons:
  - n = 1: 2 electrons ( $2(1)^2 = 2$ )
  - n = 2: 8 electrons ( $2(2)^2 = 8$ )
  - n = 3: 18 electrons ( $2(3)^2 = 18$ )
  - n = 4: 32 electrons ( $2(4)^2 = 32$ )

Electrons are drawn to the nucleus, with the attraction being strongest in proximity to the nucleus.
Electrons initially fill the innermost shell, followed by the second shell, and so on.
When electrons are arranged in this manner, the atom is in its lowest energy state, referred to as the ground state.

Electron configuration describes the arrangement of electrons within the shells of an atom when it is in its ground state.
For example, a sodium atom contains 11 electrons, and its electron configuration is 2,8,1.
- This indicates that two electrons occupy shell 1, eight electrons occupy shell 2, and the remaining electron occupies shell 3.

The number of protons within the nucleus defines the element to which the atom belongs.
There are 118 distinct elements, with 26 of them being synthetic and created in laboratories rather than found naturally on Earth.
Elements can be regarded as the fundamental components from which all substances are formed.

The atomic number corresponds to the quantity of protons present in the nucleus of an atom.
- $Atomic \space number = number \space of \space protons$
Each element possesses a unique and characteristic atomic number.
For instance, all carbon atoms contain six protons, resulting in an atomic number of 6.
Oxygen atoms consistently have eight protons (atomic number of 8), while uranium atoms have 92 protons (atomic number 92).

Uranium holds the distinction of being the heaviest naturally occurring element.
Its substantial size renders its nuclei unstable.
The disintegration of these nuclei releases substantial amounts of energy, as demonstrated during the 1958 atomic bomb test.

Explain why most of an atom’s mass is due to its nucleus.
- Because protons and neutrons, located din the nucleus, are about 1800 times heavier than electrons.
Use the formula $2n^2$ to calculate the maximum number of electrons held by shell 5 (n = 5).
- $2 * 5^2 = 50$
Demonstrate how to write electron configurations by writing them for the following atoms.
- lithium (with 3 electrons): 2, 1
- carbon (with 6 electrons): 2, 4
- sodium (with 11 electrons): 2, 8, 1
- chlorine (with 17 electrons): 2, 8, 7
Identify the type of atoms and the number of each type in a single molecule of:
- methane, $CH_4$ : 1 carbon atom and 4 hydrogen atoms
- nitric acid, $HNO_3$ : 1 hydrogen atom, 1 nitrogen atom and 3 oxygen atoms
- glucose, $C<em>6H</em>{12}O_6$ : 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms
- ethanoic acid (vinegar), $CH_3COOH$ : 2 carbon atoms, 4 hydrogen atoms and 2 oxygen atoms