Elements and the Periodic Table

Atoms and Elements

• Everything in the universe is composed of atoms, the basic building blocks of matter.

• Not all atoms are the same; there are different types of atoms called elements, each with unique properties.

• Each element has a unique set of physical and chemical properties that define its behavior.

• Examples of elements: Oxygen (essential for respiration), carbon (the backbone of organic molecules), gold (a precious metal), bismuth (used in pharmaceuticals), xenon (a noble gas used in lighting), and osmium (one of the densest elements).

Atomic Number (Z)

• A particular element is identified by the number of protons in its atoms, which is fundamental to its identity.

• The atomic number (Z) represents the number of protons in the nucleus of an atom and is unique to each element.

• Example: Helium has an atomic number of 2, meaning every helium atom has two protons in its nucleus.

• Example: Iron has an atomic number of 26, so every iron atom has 26 protons, giving it distinct properties.

Neutral Atoms and Electrons

• The atomic number also indicates the number of electrons in a neutral atom of an element, maintaining electrical neutrality.

• Equal and opposite charges cancel each other out; a neutral atom has an equal number of protons (charge of +1) and electrons (charge of -1), resulting in no net charge.

• Helium atom (atomic number 2) has two electrons orbiting the nucleus, balancing the two protons.

• Iron atom (atomic number 26) has 26 electrons in various energy levels around the nucleus.

Periodic Table

• All known elements are organized according to their atomic numbers in the periodic table, a tabular display of the elements.

• Elements are listed in order of increasing atomic number from left to right and top to bottom, providing a systematic arrangement.

• Elements are organized into columns (groups) based on their properties, with elements in the same group exhibiting similar characteristics.

• Elements in the same column tend to have similar physical and chemical properties due to having the same number of valence electrons.

Chemical Symbols

• Every element is represented by a chemical symbol, a unique one or two-letter abbreviation on the periodic table for easy identification.

• Many chemical symbols are based on the English name for an element (e.g., Hydrogen = H, Aluminum = Al), making them intuitive.

• Some chemical symbols are based on the Latin name for the element (e.g., Lead = Pb, from plumbum), reflecting historical nomenclature.

• If a chemical symbol has two letters, the second letter is lowercase to distinguish it from other elements.

Element Information on the Periodic Table

• Each element's box on the periodic table contains its atomic number, chemical symbol, and name, providing key information at a glance.

• Example: Nitrogen's box shows:

  • Atomic number: 7 (number of protons and electrons in a neutral atom)

  • Chemical symbol: N

  • Name: Nitrogen

• Often, the atomic mass is also listed at the bottom of the box, indicating the average mass of atoms of that element.

Using the Periodic Table

• If we know one detail about an element (atomic number, chemical symbol, or name), we can often use the periodic table to find out other details, making it a valuable reference tool.

• Example: Phosphorus

  • Looking at the periodic table reveals its atomic number is 15 and its chemical symbol is P.

• Example: Hg

  • Locating Hg on the periodic table shows it is Mercury, and its atomic number is 80 (meaning it has 80 protons).

Isotopes and Atomic Mass

• Isotopes are variants of an element that have the same number of protons but different numbers of neutrons.

• The atomic mass of an element is the weighted average mass of all its isotopes.

• Example: Carbon has two stable isotopes: carbon-12 (^{12}C) and carbon-13 (^{13}C). Most carbon atoms are carbon-12, so the atomic mass of carbon is close to 12.

Ions

• Ions are atoms or molecules that have gained or lost electrons, resulting in a net electric charge.

• Cations are positively charged ions formed by losing electrons.

• Anions are negatively charged ions formed by gaining electrons.

• Example: Sodium (Na) can lose an electron to form a sodium ion (Na^{+}), a cation.

• Example: Chlorine (Cl) can gain an electron to form a chloride ion (Cl^{-}, an anion.

Compounds and Molecules

• Compounds are substances formed when two or more elements are chemically bonded together.

• Molecules are the smallest units of a compound that retain the chemical properties of that compound.

• Example: Water (H_{2}O) is a compound formed from hydrogen and oxygen atoms.

• Example: Sodium chloride (NaCl) is a compound formed from sodium and chlorine atoms.

Chemical Bonds

• Chemical bonds are the attractive forces that hold atoms together in molecules and compounds.

• Ionic bonds are formed through the transfer of electrons between atoms.

• Covalent bonds are formed through the sharing of electrons between atoms.

• Example: In sodium chloride (NaCl), an ionic bond is formed between Na^{+} and Cl^{-}.

• Example: In water (H_{2}O$$), covalent bonds are formed between oxygen and hydrogen atoms.

States of Matter

• Matter exists in different states, including solid, liquid, gas, and plasma.

  • Solid: Has a fixed shape and volume.

  • Liquid: Has a fixed volume but takes the shape of its container.

  • Gas: Has no fixed shape or volume.

  • Plasma: An