atom

Examples of atom in the following topics:

• Converting between Moles and Atoms

  • $x \ moles \cdot \frac {6.022\times10^{23} atoms}{1 \ mole} = y \ atoms$
  • $6 \ moles \cdot \frac {6.022\times 10^{23} atoms}{1 \ mole} = 3.61\times 10^{24} atoms$
  • $\frac{x \ atoms}{6.022\times 10^{23} \frac{atoms}{1 \ mole}} = y \ moles$
  • $x \ atoms \cdot \frac{1 \ mole}{6.022\times 10^{23} \ atoms} = y \ moles$
  • $3.5 \times 10^{24} \ atoms \cdot \frac{1 \ mole}{6.022\times 10^{23} \ atoms} = 5.81 \ moles$

• Hydrogen Bonding

  • A hydrogen bond is the electromagnetic attraction created between a partially positively charged hydrogen atom attached to a highly electronegative atom and another nearby electronegative atom.
  • A hydrogen atom attached to a relatively electronegative atom is a hydrogen bond donor.
  • In the molecule ethanol, there is one hydrogen atom bonded to an oxygen atom, which is very electronegative.
  • This hydrogen atom is a hydrogen bond donor.
  • Ethanol contains a hydrogen atom that is a hydrogen bond donor because it is bonded to an electronegative oxygen atom, which is very electronegative, so the hydrogen atom is slightly positive.

• Average Atomic Mass

  • The atomic number of an element defines the element's identity and signifies the number of protons in the nucleus of one atom.
  • For example, stable helium atoms exist that contain either one or two neutrons, but both atoms have two protons.
  • These different types of helium atoms have different masses (3 or 4 atomic mass units), and they are called isotopes.
  • Chlorine consists of two major isotopes, one with 18 neutrons (75.77 percent of natural chlorine atoms) and one with 20 neutrons (24.23 percent of natural chlorine atoms).
  • The atomic number of chlorine is 17 (it has 17 protons in its nucleus).

• Early Ideas about Atoms

  • In 1661, Boyle presented a discussion of atoms in his The Sceptical Chymist.
  • Dalton's experiments with gases led to some of the earliest measurements of atomic masses and a concept of atomic structure and reactivity.
  • Dalton's atomic theory contained the following ideas:
  • Atoms are indestructible.
  • Describe the early developments leading to the modern concept of the atom

• Single Covalent Bonds

  • Single covalent bonds are sigma bonds, which occur when one pair of electrons is shared between atoms.
  • An atomic orbital is defined as the probability of finding an electron in an area around an atom's nucleus.
  • Regardless of the atomic orbital type, sigma bonds can occur as long as the orbitals directly overlap between the nuclei of the atoms.
  • A single covalent bond can be represented by a single line between the two atoms.
  • These are all possible overlaps between different types of atomic orbitals that result in the formation of a sigma bond between two atoms.

• Overview of Atomic Structure

  • Atoms are made up of particles called protons, neutrons, and electrons, which are responsible for the mass and charge of atoms.
  • This can be determined using the atomic number and the mass number of the element (see the concept on atomic numbers and mass numbers).
  • In these atoms, the positive and negative charges cancel each other out, leading to an atom with no net charge.
  • The electrons that surround all atoms are negatively charged and cause atoms to repel one another, preventing atoms from occupying the same space.
  • Elements, such as helium, depicted here, are made up of atoms.

• Oxidations & Reductions

  • Carbon atoms may have any oxidation state from –4 (e.g.
  • Bonds to other carbon atoms are ignored.
  • This count should be conducted for each carbon atom undergoing any change during a reaction.
  • If the number of hydrogen atoms bonded to a carbon increases, and/or if the number of bonds to more electronegative atoms decreases, the carbon in question has been reduced (i.e. it is in a lower oxidation state).
  • Carbon atoms colored blue are reduced, and those colored red are oxidized.

• Atomic Number and Mass Number

  • For example, carbon's atomic number (Z) is 6 because it has 6 protons.
  • The number of electrons can also be different in atoms of the same element, thus producing ions (charged atoms).
  • Given an atomic number (Z) and mass number (A), you can find the number of protons, neutrons, and electrons in a neutral atom.
  • Its average atomic mass is 12.11.
  • Determine the relationship between the mass number of an atom, its atomic number, its atomic mass, and its number of subatomic particles

• Atomic Radius

  • Depending on context, the term atomic radius may apply only to isolated atoms, or also to atoms in condensed matter, covalently bound in molecules, or in ionized and excited states.
  • These trends of the atomic radii (and of various other chemical and physical properties of the elements) can be explained by the electron shell theory of the atom.
  • The way atomic radius varies with increasing atomic number can be explained by the arrangement of electrons in shells of fixed capacity.
  • A chart showing the atomic radius relative to the atomic number of the elements.
  • Predict the relative atomic sizes of the elements based on the general trends in atomic radii for the periodic table.

• John Dalton and Atomic Theory

  • Dalton introduced a theory that proposed that elements differed due to the mass of their atoms.
  • Dalton found an atomic theory of matter could elegantly explain this common pattern in chemistry - in the case of Proust's tin oxides, one tin atom will combine with either one or two oxygen atoms.
  • A chemical reaction results in the rearrangement of atoms in the reactant and product compounds.
  • In addition, the discovery of subatomic particles has shown that atoms can be divided into smaller parts.
  • However, Dalton's importance in the development of modern atomic theory has been recognized by the designation of the atomic mass unit as a Dalton.