The Atom and Chemical Bonding Theories

• Unidad 2 focuses on the Atom, Periodic Table, and Theories of Chemical Bonding

Atom

• An atom serves as the minimal expression of matter
• Democritus, around 460-370 BC, and other philosophers considered the atom indivisible
• The term "atom" itself means indivisible
• A new atomic theory was proposed in the 17th century by John Dalton (1803-1807)
• Dalton's atomic theory rests on the following four postulates:
  • Each element consists of extremely small particles called atoms
  • All atoms of a given element are identical. However, atoms of one element are different from atoms of all other elements
  • Atoms of one element cannot be transformed into atoms of another element by chemical reactions; atoms are neither created nor destroyed in chemical reactions
  • Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms
• Atoms consist of subatomic particles, which can be elementary or composite
• Elementary particles are Quarks, Leptones, Bosons, and Electrons
• Peter Higgs discovered the Higgs mechanism, explaining the origin of mass in elementary particles; the particle associated with this mechanism is called the Boson of Higgs or "God particle"
• The nucleus of an atom contains protons (positive charge) and neutrons (neutral charge)
• The region surrounding the nucleus is called the cortex and contains electrons (negative charge)
• Mass of a proton (P): 1.6x10^-24 g
• Mass of an electron (e): 9.10938x10^-28 g
• The mass of a neutron (N) is aproximately equal to the mass of a proton
• Chemical elements consist of atoms of the same class with the same number of electrons and protons that group together
• Atoms grouped together are organized into the periodic table by families and similar characteristics
• Molecules consist of clustered atoms of distinct chemical elements, forming stable, electrically neutral groups
• Molecules may have two or more atoms and are characteristic of covalent bonding
• Water is an example of a molecule
• The atomic number (Z) is the number of electrons or protons in a chemical element
  • 2P+ or 2e- = atomic number = Z
• In a neutral atom, the number of electrons equals the number of protons (Z = e- = P+)
• The mass number (A) is the total mass of protons and neutrons in an atom's nucleus
• The mass of an electron is negligible in comparison
  • A = Number of mass = N + Z
• An Isotope is a variant of a chemical element with the same number of protons, indicated by the atomic number, but a different number of neutrons
• Isotopes have different atomic masses and different properties

Periodic Table

• The periodic table arranges chemical elements by their properties and atomic numbers
• Chemical elements are pure substances with atoms having the same number of protons in their nucleus
• Elements are arranged in horizontal rows called periods, based on the energy levels of their electrons, and in vertical columns called groups or families, based on the number of electrons in their valence shell
• There are energy levels around the nucleus where electrons are located based on their energy:
  • Level 1 (K): s sublevels, accommodates up to 2 electrons
  • Level 2 (L): s and p sublevels, accommodates up to 8 electrons
  • Level 3 (M): s, p, and d sublevels, accommodates up to 18 electrons
  • Level 4 (N): s, p, d, and f sublevels, accommodates up to 32 electrons
  • Level 5 (O): s, p, d, and f sublevels, accommodates up to 50 electrons
  • Level 6 (P): s, p, d, and f sublevels, accommodates up to 72 electrons
  • Level 7 (Q): s, p, d, and f sublevels, accommodates up to 98 electrons
• The maximum number of electrons in a level can be calculated using the formula:
  • Cap. max. e- = 2 * n^2, where n = # level
• Groups or families are organized based on the number of electrons in their valence shell:
  • I: Alkali metals; Valence shell: S1
  • II: Alkaline earth metals; Valence shell: S2
  • III - XII: Transition metals; Valence shell: dx
  • XIII: Boron or Terra family; Valence shell: S2P1 or S1p2
  • XIV: Carbonoids; Valence shell: S2p2 or S1p3
  • XV: Nitrogenoids; Valence shell: S2 p3
  • VXI: Chalcogens / Amphigians; Valence shell: S2 p4
  • XVII: Halogens; Valence shell: S2p5
  • XVIII: Noble gases; Valence shell: S2p6
• An ion is an atom or group of atoms with an electrical charge due to the loss (+) or gain (-) of one or more electrons -#P+ = #e¯
• Atoms or molecules in nature may have positive or negative charges
• Anion: A negatively charged atom due to the gain of electrons
• Cation: A positively charged atom due to the loss of electrons
• Anion + Cation = Neutral Compounds (Salts)
• Molecules consist of two or more atoms of the same or different kinds
• Elements such as H2, N2, O2, F2, Cl2, Br2, and I2 exist naturally as diatomic molecules
• Molecules with more than two atoms are polyatomic molecules
• Mole, defined as the amount of a substance
  • The number of moles does not depend on the material
  • 1 mol = 6.022 x 10^23 atoms (Avogadro's Number)
  • 1 mole of Ideal Gas = 22.4 L
• Periodic properties vary along the periodic table and within groups or families -Ionization Energy or Potential -Atomic and Ionic Radius -Electronegativity -Electronic Affinity -Metallic Character
• Ionization energy or potential is the amount of energy required to remove an electron from a gaseous atom or ion
• This process converts the atom into a positive ion, or cation
• Factors indicating the ability to retain its electrons :
  • Atom size: larger atoms have electrons further from the nucleus, requiring less energy for removal
  • Nucelar charge: Atoms with more protons have a higher attrection making it harder for electron removal
  • Shielding effect: inner electrons "protect" the outer electrons from the attraction of the nucleus, this reduces the ionization energy
• Atomic radius is half the distance between the nuclei of two identical atoms bonded together
• Ionic Radius It is the average distance from the nucleus of an ion to the outermost electron in its electronic cloud
  • Cations have a smaller ionic radius
  • Anions have a larger ionic radius
• Electron affinity indicates how easily an atom accepts an electron in the gaseous phase to form an anion
  • Energy is released (-) when an electron is accepted
  • Energy is absorbed (+) if an electron is rejected
  • Atom size: The smaller the atom is, the better electron affinity
  • Nuclear charge: the great the protons, the better electron affinity
  • Electronic configuration: Atoms with stable electronic configurations, such as noble gases, have a low electronic affinity
• Electronegativity (X) signifies an atom's ability to attract shared electrons in a chemical bond; it is fundamental to understand the polarity of bonds and the chemical behavior of compounds
  • Measured from the Pauling scale
  • Flourine (F) has the highest electronegativity at 3.98
  • Cesium has the lowest electronegativity at 0.79 -Electronegativity measures an atoms trending attraction to its electrons instead of an absolute measure
  • Atom Size: smaller atoms have smaller nucleaus, this causes attractions toward shared atoms during electron bonding
  • Effective Nucleus charge: Atoms with more protons can hold electrons better
  • Electronic Configuration: Electrons that have neared their valance requirements usually have high electronegativity
• Metallic Character describes how closely an element resembles a metal and is related to the loss of electrons
  • ionzation energy: Elements that have low ionization energy have a metal characteristic because they easily give up an electron.
  • Atom sizes: bigger atoms have valance elctrons, meaning they facilitate electron loss
  • Electronegativity: Elements with low eletronegativity also are metals because it means that you wont attract those electrons

Metallic Characteristics Comparison

• Metals:
  • High electrical and thermal conductivity
  • High malleability and ductility
  • High metallic character
  • Examples: Iron (Fe), Gold (Au)
• Non-Metals:
  • Poor conductors of electricity and heat
  • Tend to gain electrons rather than lose them
  • Low metallic character
  • Examples: Oxygen (O), Sulfur (S)
• Metalloids:
  • Have intermediate properties between metals and nonmetals
  • Example: Silicon (Si)

Intermolecular Forces

• Refers to the attraction forces in particles
• Is the condensation of molecules that later give solids or liquid like matter
• There are two types
  • Intermolecular: These forces keep molecules together, but they are relatively weak and they give responsible macro properties in matter
  • Intramolecular: Keep the atoms together of the same molecule while also holding great force
• There are two types of intermolecular forces which are called Van Der Waals
  • Dipole-Dipole: Polar molecules with attractive forces
  • Dipole-Dipole Induced: Non polar molecules with attractive forces
  • London descension- Molecules with small attractive force
• All this relates to hydrogen

Chemical Bonds

• Forces that keep units that atoms maintain in molecules with stable compounds
• The Lewis rule has its molecules maintain the octet of elctrons

Theories of Enlaces

• Science models can be used to explain how and why atoms combine to make molecules
• Covalent links when atoms share electrons
• Enlace de valencia (TEV)
• electrons are shared to create a electron valence (capa de valencia)
• Teoría de Repulsión de Pares de Electrones de la Capa de Valencia (TRPECV)
• Electrons are used in atoms to for geometry
• Enlace Metálico
• electrons are found and create a network for desolazation of those electrons
• Modelo de Bandas
• its specific for semiconducters

Orbitales

• Defines quantum numbers and orientation of atom
  • Numero cuanticio:Principle number that can describe the orbitals. n =1,2,3…
  • Describe the energy vales for the orbital size
  • Numero cuanticio, secundario (azimuth): Defines the the way that orbitals form d=2
    • L shows the way
  • Número cuántico magnético (m₁) defines the spaces that are presented during those vales with L (0 or 1)\
• In nature we find things to be esferical, and they are located more Interno
• While the “P” has lobe shaped structures

Facts

• Orbialtes can hold at most 2 electrons
• Electrons distribute to orbital in order
  • Regras de Alfanbau
  • Pauli Exclustion
  • Hund Regla

Configuracion Electronica

• Each electron has its own quantum number for orbitals
• If the molecule has more electrons, that will show how it distributes to the atomic models of atomes

Examples:

• Type “S” = accepts two electrons per atom
• Type “P” = Accpets six electrons per atom
• Type “D” = Accepts 10 electrons per atom
• The more that is accepted equals the stability of that molecule

Hibridation

• Atomic oribalets has certain vales for quantum
• Those with high energy will help to form a hybrid

Facts:

• Sp is usually formed with energy
• In this new form all electrons will have different form and energy
• BeF2 is usually found -The type “2” is usually “sp” when hibriding
• If the hybrid continues at its state that means molecules are most likely to exist
• BF3 is very popular with this situation