Atoms and Elements Quiz

Atoms and Elements

• Matter is anything that takes up space and has mass
• Matter is made of elements
• Elements are substances that cannot be broken down into simpler substances through ordinary chemical means
• Only 92 naturally occurring elements serve as the building blocks of all matter
• 95% of living organisms' weight is composed of six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur
• Elements are basic to life

Organization of Living Things

• Organ: Composed of tissues that function together for a specific task
• Tissue: A group of cells with a common structure and function
• Cell: The structural and functional unit of all living things
• Molecule: A union of two or more atoms of the same or different elements
• Atom: The smallest unit of an element, composed of electrons, protons, and neutrons

Structure of an Atom

• Electrons orbit the nucleus at particular energy levels; electron shells or orbitals

• Valence shell: the outer electron shell

• Most elements do not exist as single atoms in nature

• Atom is the smallest piece of an element displaying the element's properties

• Atomic number is the number of protons

• Atomic mass is the sum of protons and neutrons

Molecules and Compounds

• Molecules form when two or more atoms bond together
• Compounds form when molecules consist of two or more (different) elements bond together
• Molecule: The smallest part of a compound that still has the characteristics of the compound
• Reaction: A process where two or more substances interact with each other
• Chemical reaction: Energy may be given off or absorbed

Types of Bonding

• Bonding occurs when electrons are transferred, shared, or attracted to another element, molecule, or compound
• Electrons possess energy, and the bonds between atoms also contain energy
• Organisms are directly dependent on chemical-bond energy to maintain their organization
• Types of Bonding:
  • Metallic
  • Ionic
  • Covalent
    • Nonpolar
    • Polar
  • Hydrogen

Ionic Bonding

• Ionic bonding occurs between a metal and a non-metal
• Ions are charged particles that form when electrons are transferred from one atom to another
• Ionic compounds are held together by an attraction between oppositely charged ions called an ionic bond

Covalent Bonding

• In covalent bonds, atoms share electrons allowing each atom to have a completed outer shell
• A covalent bond is between two non-metals
• Types of Covalent Bonds:
  • Nonpolar covalent bonds: Electron sharing is equal
  • Polar covalent bonds: Electron sharing is unequal

Hydrogen Bonding

• A hydrogen bond forms between a slightly positive hydrogen atom of one molecule and a slightly negative O, N or F of another molecule

Chemistry of Water

• Water is a polar molecule
• Due to hydrogen bonding, water molecules cling together
• Without hydrogen bonding: melting point (-90° C), vaporization (-100° C)

Properties of Water

• Properties of Water:
  • Water is a solvent
  • Water has a high heat capacity
  • Water has a high heat of vaporization
  • Water is cohesive
  • Water is adhesive
  • Water has a high surface tension
  • Frozen water is less dense than liquid water

Acids and Bases

• When water ionizes, it releases an equal number of H+ and OH- ions
• Acids release H+ ions when they dissociate in water
• Bases either take up H+ ions or release OH- ions

pH Scale

• pH scale ranges from 0-14
• pH below 7 is acidic, pH above 7 is alkaline, and pH of 7 is neutral
• pH of sweat is between 4.5 and 7.0
• pH of tea varies depending on the type of tea

Buffers and pH

• A buffer is a chemical(s) that keep pH within normal limits
• In animals, the pH of body fluids is maintained within a narrow range
• The body has built-in mechanisms to prevent pH changes, and buffers are the most important of these mechanisms
• Bicarbonate ions (HCO3) and carbonic acid(H2CO3) found in human blood buffer the pH of blood to 7.4