Atoms and Atomic

Structהוא אלבוםDefinition and Structure of the Atom

An atom is the smallest particle of an element that retains the properties of that element. Atoms are the fundamental building blocks of matter.

• Nucleus: The dense central core of the atom, containing protons and neutrons.

• Proton (p+): A positively charged particle found inside the nucleus.

• Neutron (n0): A particle found in the nucleus with no electric charge.

• Electron (e-): A negatively charged particle that orbits the nucleus in defined energy levels.

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Energy Levels and Electron

Configuration

Electrons occupy specific energy levels (also called shells) around the nucleus. Each energy level can hold a certain maximum number of electrons:

• The first energy level can hold up to 2 electrons.

• The second energy level can hold up to 8 electrons.

• The third energy level can hold up to 18 electrons.

For an atom to be stable, its outermost energy level (valence shell) should be full or satisfy the octet rule (8 electrons for most main-group elements).

• Example: An atom with 8 electrons: 2 in the first level, 6 in the second. The second level is not full, so the atom is not fully stable.

• Electron Configuration Example: For an atom with 10 electrons (Neon): 2 in the first level, 8 in the second. This is a stable configuration.

Elements and the Periodic Table

Definition of Elements

An element is a pure substance that cannot be broken down into simpler substances by chemical means. Each element is defined by its number of protons.

• There are about 90 naturally occurring elements.

• All elements are listed in the Periodic Table.

• Only about 25 elements are essential for living things; the majority of human body mass is composed of carbon (C), hydrogen (H), nitrogen (N), and oxygen (O).

Atomic Number and Atomic Mass

• Atomic Number (Z): The number of protons in the nucleus of an atom. It is unique for each element and determines the element's identity.

• Atomic Mass (A): The total number of protons and neutrons in the nucleus.

Determining Subatomic Particles:

• Number of protons = atomic number

• Number of electrons = atomic number (in a neutral atom)

• Number of neutrons = atomic mass - atomic number

• Example: Carbon (atomic number 6, atomic mass 12): 6 protons, 6 electrons, 6 neutrons.

Ions and Isotope

• Ion: An atom or molecule with a net electric charge due to the loss or gain of electrons.

• Number of protons does not change; only electrons are gained or lost.

• Example: Na+ has 11 protons and 10 electrons.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Examples: Carbon-12 (6p/6n), Carbon-13 (6p/7n), Carbon-14 (6p/8n).

Chemical Bonds and Compounds

How Elements Combine

• Compound: A substance made of two or more different elements bonded together (e.g., NaCl, H2O).

• Molecule: A group of atoms held together by covalent bonds (e.g., O2).

Covalent Bonds

• Formed when two atoms share electrons.

• Polar Covalent Bond: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Nonpolar Covalent Bond: Electrons are shared equally (e.g., H2, ethane).

Ionic Bonds

• Formed when atoms transfer electrons, resulting in oppositely charged ions that attract each other (e.g., Na+ + Cl- → NaCl).

Hydrogen Bonds

• Weak bonds that form between a hydrogen atom (already covalently bonded to a highly electronegative atom) and another electronegative atom.

• Important in holding water molecules together and stabilizing large biological molecules like proteins.

Properties of Water

Polarity and Hydrogen Bonding

• Water is a polar molecule due to the uneven distribution of electrons between oxygen and hydrogen atoms.

• Oxygen has a higher electronegativity, resulting in a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.

• Hydrogen bonds form between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.

Key Properties of Water

• Cohesion: Attraction between molecules of the same substance (e.g., water molecules stick together).

• Adhesion: Attraction between molecules of different substances (e.g., water and glass, causing a meniscus and capillary action).

• High Specific Heat Capacity: Water can absorb large amounts of heat due to hydrogen bonding, helping to regulate temperature.

• Evaporative Cooling: As water evaporates, it removes heat (e.g., sweating).

• Versatile Solvent: Water dissolves many substances due to its polarity, making it an excellent solvent in biological systems.

Solutions

• Solution: A homogeneous mixture of two or more substances.

• Solute: The substance that is dissolved (e.g., iced tea mix).

• Solvent: The substance that does the dissolving (e.g., water).

• In biological systems, water is almost always the solvent.

Acids, Bases, and pH

pH Scale

• The pH scale measures the concentration of hydrogen ions (H+) versus hydroxide ions (OH-) in a solution.

• The scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Acid: Substance with more H+ ions (pH < 7).

• Base: Substance with more OH- ions (pH > 7).

• Examples: Pure water (pH 7), soda (pH 3), hair remover (pH 13).

Chemical Equations

Structure of Chemical Equations

• Chemical equations represent the reactants and products in a chemical reaction.

• Reactants: Substances that undergo change.

• Products: Substances formed as a result of the reaction.

• Chemical Equation Example:

• Coefficients: Numbers in front of compounds/elements indicating the number of molecules or atoms involved (e.g., 6CO2 means 6 molecules of CO2).

• Subscripts: Numbers written below and to the right of element symbols indicating the number of atoms in a molecule (e.g., H2O has 2 hydrogen atoms).

Table: Comparison of Subatomic Particles

Additional info: Some details, such as the maximum number of electrons in higher energy levels and the full chemical equation for photosynthesis, were inferred for completeness.