Atoms and molecules

• What is an atom?

  The smallest unit of a chemical element that maintains the element's chemical properties, consisting of protons, neutrons, and electrons
• What are protons?


  Positively charged subatomic particles located in the nucleus of an atom
• What are neutrons?


  Neutral subatomic particles found in the nucleus of an atom
• What are electrons?


  Negatively charged subatomic particles that orbit around the nucleus of an atom
• What is the atomic number (Z) of an atom?

  The number of **protons** in the nucleus of an atom, which uniquely identifies a chemical element
• For a carbon atom with 6 protons and 6 neutrons, what are its atomic number and mass number?


  Atomic number (Z): 6 (number of protons)

  Mass number (A): 12 (6 protons + 6 neutrons)
• What is the mass number (A) of an atom?

  The total number of **protons and neutrons** in the nucleus of an atom
• How do you calculate the number of neutrons in an atom?

  **Mass number (A) - Atomic number (Z) = Number of neutrons**
• What is an isotope?

  Atoms of the same element with the same number of protons but different numbers of neutrons. They have the same atomic number (Z) but different mass numbers (A).
• An atom has 11 protons and 12 neutrons. What is its mass number?

  23 (11 protons + 12 neutrons = mass number 23)
• What makes isotopes of an element different from each other?

  The number of neutrons in their nucleus, while maintaining the same number of protons
• How do isotopes of an element differ in their chemical properties?

  They have nearly identical chemical properties because they have the same number of electrons and proton configuration
• What is the notation for representing an isotope?

  $^A_Z X$, where A is the mass number, Z is the atomic number, and X is the element symbol
• What is the difference between a neutral atom and an ion?

  A neutral atom has equal numbers of protons and electrons, while an ion has an unequal number of protons and electrons, resulting in a net electrical charge.
• If sodium (Na) has 11 protons and loses 2 electrons, what is its ion charge?

  Na would become Na²⁺ (a cation with a +2 charge) because it now has 11 protons but only 9 electrons
• How do you calculate the charge of an ion?

  Charge = Number of protons - Number of electrons
• What is the difference between a cation and an anion?

  A cation is a positively charged ion (loses electrons), while an anion is a negatively charged ion (gains electrons)
• What is the fundamental difference between an atom and a molecule?

  An atom is the smallest unit of an element, while a molecule is a combination of two or more atoms chemically bonded together.
• How many atoms are in a water molecule (H₂O)?

  3 atoms: 2 hydrogen atoms and 1 oxygen atom
• Can a molecule be made of atoms from different elements?

  Yes, molecules can be composed of atoms from the same or different elements. For example, H₂O (water) contains two different elements.
• What makes an atom different from a molecule in terms of properties?

  An atom cannot be divided without changing the element's properties, while a molecule has different properties from its constituent atoms due to chemical bonding.
• Give an example of a molecule made of atoms from the same element

  Oxygen molecule (O₂), which consists of two oxygen atoms bonded together