Science 2 chapter
Elements Overview
Elements: Pure substances that cannot be broken down into simpler substances. Made of one kind of atom.
Matter exists in various forms on Earth, in the solar system, and beyond.
Chemical Symbols
Over 115 elements exist, with around 92 naturally occurring and others being synthetic.
Chemists use international symbols for elements.
Chemical symbols consist of one or two letters:
Single letter: Always capitalized (e.g., H).
Two letters: First capitalized, second lowercase (e.g., He).
Common Elements
Metals: Hard, shiny, malleable, ductile, good conductors of heat and electricity.
Non-Metals: Usually gases or brittle solids, poor conductors and lack metallic properties.
Key elements include: Hydrogen, Iron, Oxygen, Sodium, Chlorine, Mercury, Silver, Silicon.
Hydrogen (H)
Colorless, odorless, tasteless, highly flammable.
Lightest element, makes up over 90% of the universe and is highly reactive.
Predominantly found on Earth as part of water (H2O).
Used for producing ammonia for fertilizers, and as a fuel in hydrogen cars (producing water as a by-product).
Iron (Fe)
Strong metal, particularly when combined with carbon to form steel.
Ductile and can be drawn into thin wires.
Susceptible to rusting in the presence of water and oxygen; preventive measures include painting.
Oxygen (O)
Non-metal and essential for respiration; a product of photosynthesis.
Comprises about 21% of the atmosphere and a major component of water.
Key element in the composition of Earth's crust.
Sodium (Na)
Soft metal, can be cut with a knife.
Reacts violently with water to release hydrogen and heat, posing explosion risks.
Used in some chemical reactions such as producing drain cleaner.
Chlorine (Cl)
Pale yellow-green gas, used for disinfection in swimming pools and water supplies.
Highly reactive in concentrated forms, yet combines with sodium to form table salt (NaCl).
Mercury (Hg)
Unique metal as it is liquid at room temperature.
Conducts electricity well and is used in specialized equipment like sparkless switches.
Highly toxic, with mercury vapor posing severe health risks.
Silver (Ag)
Malleable, ductile, and a superior conductor of heat and electricity.
Used in electronics and jewelry, also enhances sound quality in musical instruments.
Silicon (Si)
Second most common element in the Earth's crust.
Known for its use as a semiconductor in electronics, particularly in computer chips.
Combines with oxygen to form minerals like quartz and opal.
The Periodic Table
Organizes elements in rows and columns based on atomic number and properties.
Mendeleev's periodic table from 1867, predicted undiscovered elements by leaving gaps.
Atomic Numbers and Mass
Atomic Number: Number of protons in an atom, determines the element.
Atomic Mass: Average mass of an element’s atoms.
Mass Number: Total of protons and neutrons.
Metals, Non-Metals, and Metalloids
Metals: Hard, shiny, malleable, and good conductors of electricity. Left of the staircase in the periodic table.
Non-metals: Not shiny, poor conductors, typically gases or brittle solids.
Metalloids: Share properties of both metals and non-metals, located along the staircase.
Chemical Families
Alkali Metals (Group 1): Highly reactive, low melting points.
Alkaline Earth Metals (Group 2): Reactive but less so than alkali metals; burn brightly in air.
Halogens (Group 17): Highly reactive non-metals, with varied states at room temperature.
Noble Gases (Group 18): Unreactive gases with filled valence shells, used in lighting.
Reaction and Stability of Elements
Elements react to achieve stable electron configurations, often similar to noble gases.
Valence Electrons: Electrons in the outermost shell influencing reactivity.
Noble gases do not react because they have full valence shells.