Education/Public Outreach Cosmic Chemistry: An Elemental QuestionAn atom is the basic structure from which all matter is composed, in thesame manner as a brick is basic to the structure of a wall. Although atomsare too small to be seen with our eyes, scientists have long had indirectevidence for the existence of atoms.
Education/Public Outreach Cosmic Chemistry: An Elemental Question Model of Proton, Neutron, and ElectronAtoms are made of small particles called protons, neutrons, and electrons.Each of these particles is described in terms of measurable properties,including mass and charge. Mass is the amount of matter that an objectcontains. The proton and neutron have roughly the same mass and haveapproximately one thousand times the mass of the electron. The proton andelectron have equal, but opposite, electrical charges. A neutron does not havean electrical charge.
Education/Public OutreachCosmic Chemistry: An Elemental Question If the proton and neutron were enlarged, and each had the approximate mass of a hippopotamus, the electron, enlarged to the same scale, would have less mass than an owl.
Education/Public Outreach Cosmic Chemistry: An Elemental QuestionMost of an atom is emptyspace. The nucleus of theatom contains almost all ofthe mass of the atom. Agreatly enlarged atommight look like a marble(the nucleus) inside anempty football stadium.(The electron probabilitycloud is where the electronis likely to be). Electron Probability Cloud Around a Nucleus
Education/Public Outreach Cosmic Chemistry: An Elemental Question Diagram Comparing a Beryllium Atom and a Positively-Charged Beryllium IonThe attractive electric force between the positively-charged protons in thenucleus and the negatively-charged electrons around the nucleus holds theatom together. Atoms containing the same number of protons and electronshave no net charge. Atoms that have extra electrons or are missingelectrons have a net electrical charge and are called ions. Ions can interactwith other ions due to the electrical attraction between opposite charges.
Education/Public Outreach Cosmic Chemistry: An Elemental Question Model of Covalent and Ionic BondsAtoms interact with other atoms by sharing or transferring electrons that arefarthest from the nucleus. These outer electrons determine the chemicalproperties of the element, such as how readily it interacts with other elementsand the allowable ratios for its combinations with other substances.
Education/Public Outreach Cosmic Chemistry: An Elemental Question An element is a substanceElement Symbol Relative % of made up of a single type of Earth’s Mass atom. It can’t be broken intoOxygen O 46.6 simpler components bySilicon Si 27.7 chemical processes. ThereAluminum Al 8.1 are 92 naturally occurringIron Fe 5.0Calcium Ca 3.6 elements. They may be solids, liquids, or gases. TheSodium Na 2.8 elements are distributed unevenly, with some muchPotassium K 2.6 more common than others.Magnesium Mg 2.1 The ten most abundantTitanium Ti 0.4 elements on earth make upHydrogen H 0.1 more than 96% of our planet.
Education/Public Outreach Cosmic Chemistry: An Elemental QuestionGold is one example of an element. A bar of gold can be shaved into gold dust, and still be How fine can the dust recognizable as gold. become and still be considered gold?The smallest particle that would still have theproperties associated with gold is an atom.How small is an atom? Consider that asmall gold coin may contain over20,000,000,000,000,000,000,000 atoms.
Atomic mass and atomic number• The atomic mass (ma) is the mass of a specific isotope, most often expressed in unified atomic mass units (amus). The atomic mass is the total mass of protons, neutrons and electrons in a single atom.• The atomic number (also known as the proton number) is the number of protons found in the nucleus of an atom. Atomic number Atomic mass
Using the periodic table to find information• The periodic table gives you lots of information. One of the typical things that you must know is how to find the number of protons, neutrons and electrons in a given element. In order to do this:Step 1:- Find the element in the periodic table.- Find the atomic mass and the atomic number. Atomic number Atomic mass
Number of protons• Step 2 - The Number of Protons is...The atomic number is the number of protons in an atom of an element. In our example, kryptons atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus.The interesting thing here is that every atom of krypton contains 36 protons. If an atom doesnt have 36 protons, it cant be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine.
Number of electrons• Step 3 - The Number of Electrons is...By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. In our example, an atom of krypton must contain 36 electrons since it contains 36 protons.An atom can gain or lose electrons, becoming what is known as an ion. An ion is nothing more than an electrically charged atom. Adding or removing electrons from an atom does not change which element it is, just its net charge.
Number of neutrons• Step 4 - The Number of Neutrons is...1. Round the atomic mass to the nearest whole number. To get the mass number. The mass number is a count of the number of particles in an atoms nucleus. Remember that the nucleus is made up of protons and neutrons. So, if we want, we can write: Mass Number = (Number of Protons) + (Number of Neutrons)For krypton, this equation becomes: 84 = (Number of Protons) + (Number of Neutrons)If we only knew how many protons krypton has, we could figure out how many neutrons it has. Wait a minute... We do know how many protons krypton has! We did that back in Step 2! The atomic number (36) is the number of protons in krypton. Putting this into the equation, we get: 84 = 36 + (Number of Neutrons)What number added to 36 makes 84? Hopefully, you said 48. That is the number of neutrons in an atom of krypton.
Isotopes• The interesting thing here is that adding or removing neutrons from an atom does not create a different element. Rather, it creates a heavier or lighter version of that element. These different versions are called isotopes and most elements are actually a mixture of different isotopes.