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Study Guide: Atomic Structure, Study Guides, Projects, Research of Chemistry

San José State University (SJSU)Chemistry

Study guide on atomic structure.

Typology: Study Guides, Projects, Research

2018/2019

Uploaded on 08/13/2019

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Basic Atomic Structure
•Pieces of an Atom
•All matter consists of atoms. Atoms consist of nucleus & electrons. The nucleus consists of
protons & neutrons. The properties of these are measurable; they have mass & an electrical
charge.
♦Nucleus – is positively charged due to the presence of protons.
♦Electrons – are negatively charged & orbit the nucleus.
•The nucleus has considerably more mass than the surrounding electrons. Atoms can bond
together to make molecules.
•Atoms that have an equal number of protons & electrons are electrically neutral. If the
number of protons & electrons in an atom is not equal, the atom has a positive or negative
charge & is an ion.
•Models of Atoms
•Atoms are extremely small. Atomic radius refers to the average distance between the
nucleus & the outermost electron. Models of atoms that include the proton, nucleus, &
electrons typically show the electrons very close to the nucleus & revolving around it, similar
to how the Earth orbits the sun.
•However, another model relates the Earth as the nucleus & its atmosphere as electrons,
which is the basis of the term “electron cloud.” Another description is the that electrons
swarm around the nucleus.
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Basic Atomic Structure

  • Pieces of an Atom
    • All matter consists of atoms. Atoms consist of nucleus & electrons. The nucleus consists of protons & neutrons. The properties of these are measurable; they have mass & an electrical charge. ♦ Nucleus – is positively charged due to the presence of protons. ♦ Electrons – are negatively charged & orbit the nucleus.
    • The nucleus has considerably more mass than the surrounding electrons. Atoms can bond together to make molecules.
    • Atoms that have an equal number of protons & electrons are electrically neutral. If the number of protons & electrons in an atom is not equal, the atom has a positive or negative charge & is an ion.
  • Models of Atoms
    • Atoms are extremely small. Atomic radius refers to the average distance between the nucleus & the outermost electron. Models of atoms that include the proton, nucleus, & electrons typically show the electrons very close to the nucleus & revolving around it, similar to how the Earth orbits the sun.
    • However, another model relates the Earth as the nucleus & its atmosphere as electrons, which is the basis of the term “electron cloud.” Another description is the that electrons swarm around the nucleus.
  • These atomic models are not to scale. A more accurate representation would ne a nucleus with a diameter of about 2 cm in a stadium. The electrons would be in the bleachers. This model is similar to the not-to-scale-solar system model.
  • Atomic Number
  • Atomic number of an element refers to the number of protons in the nucleus of an atom. It’s a unique identifier. It can be represented as Z. Atoms with a neutral charge have an atomic number that is equal to the number of electrons.
  • Atomic Mass
  • Atomic mass – A.K.A., the mass number. The atomic mass is the total number of protons & neutrons in the nucleus of an atom. It refers to as “A.” The atomic mass (A) is equal to the number of protons (Z) plus the number of neutrons (N). This can be represented by the equation A = Z + N. The mass of electrons in an atom is basically insignificant because it’s so small.

Electrons

  • Electrons are subatomic particles that orbit the nucleus at various levels of commonly referred to as layers, shells, or clouds. The orbiting electrons account for only a fraction of the atom’s mass. They are much smaller than the nucleus, are negatively charged, & exhibit wave-like characteristics. Electrons are part of the lepton family of elementary particles.
  • Electrons can occupy orbits that are varying distances away from the nucleus, & tend to occupy the lowest energy level they can. If an atom has all its electrons in the lowest available positions, it has a stable electron arrangement.
  • The outermost electron shell of an atom in its uncombined state is known as the valence shell. The electrons there are called valence electrons , & it’s their number that determines boding behavior. Atoms tend to react in a manner that will allow them to fill or empty their valence shells.
  • Ions
  • Most atoms are neutral since the positive charge of the protons in the nucleus is balanced by the negative charge of the surrounding electrons. Electrons are transferred between atoms when they come into contact with each other. This creates a molecule or atom in which the number of electrons does not equal number of protons, which gives it a positive or negative charge. ♦ Negative ion – is created when atom gains electrons. ♦ Positive ion – is created when an atoms loses electrons. ♦ Ionic bond – is formed between ions with opposite charges. The resulting compound is neutral. ♦ Ionization – refers to the process by which neutral particles are ionized into charged particles. Gases & plasmas can be partially or fully ionized through ionization.
  • A union between the electron structures of atoms is called chemical bonding. An atom may gain, surrender, or share its electrons with another atom it bonds with. 3 types of chemical bonding are: ♦ Ionic bonding – when at atom gains or loses electrons it becomes negatively or positively charged, turning it into an ion. An ionic bond is a relationship between 2 oppositely charged ions. ♦ Covalent bonding – atoms that share electrons have what is called a covalent bond. Electrons shared equally have a non-polar bond , while electrons shared unequally have a polar bond. ♦ Hydrogen bonding – the atom of molecules interact with a hydrogen atom in the same area. Hydrogen bonds can also form between 2 different parts of the same molecules, as in the structure of DNA & other large molecules.
  • Cation – or positive ion is formed when an atom loses 1 or more electrons.
  • Anion – or negative ion is formed when an atom gains 1 or more electrons.
  • (^) Ionic Bonding
  • The transfer of electrons from 1 atom to another is called ionic bonding. Atoms that lose or gain electrons are referred to as ions. The gain or loss of electrons will result in an ion having a positive or negative charge.

♦ Here is an example: Take an atom of sodium (NA) & an atom of chlorine (Cl). The sodium atom has a total of 11 electrons (including 1 electron in its outer shell). The chlorine has 17 electrons (including 7 electrons in its outer shell). From this, the atomic number, or number of protons, of sodium can be calculated as 11 because the number of protons equals the number of electrons in an atom. When sodium chloride (NaCl) is formed, 1 electron from sodium transfers to chlorine. Ions have charges. They are written with a plus (+) or minus (-) symbol. Ions in a compound are attracted to each other because they have opposite charges.

  • Covalent Bonding
    • Covalent bonding is characterized by the sharing of 1 or more pairs of electrons between 2 atoms or between an atom & another covalent bond. This produces an attraction to repulsion stability that holds these molecules together.
    • Atoms have the tendency to share electrons with each other so that all outer electron shells are filled. The resultant bonds are always stronger than the intermolecular hydrogen bond & are similar in strength to ionic bonds.
    • Covalent bonding occurs most frequently between atoms with similar electronegativities. Nonmetals are more likely to form covalent bonds than metals since it’s more difficult for nonmetals to liberate an electron. Electron sharing takes place when 1 species encounters another species with similar electronegativity. Covalent bonding of metals is important in both process chemistry & industrial catalysis.