Karteikarten
Building blocks basics
Karten in diesem Stapel (52)
- 1MatterIs anything that takes up space and has mass
- 2The number of elementsThere are 118 elements and 92 naturally occurring elements
- 3Percentage of elements in the atmosphereNitrogen: 78%
Oxygen: 21%
Aragon: <1%
Carbon dioxide: <1% - 4Percentage of elements in living organismOxygen: 65%
Carbon: 18%
Nitrogen:10%
Hydrogen:3% - 5Atomsbuilding block of an element, the atom. An atom is the smallest unit of matter that retains all of the chemical properties of an element.
- 6The atom includes:An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outermost region of the atom which holds its electrons in orbit around the nucleus
- 7Mass of protons and neutronsProtons and neutrons have approximately the same mass, about 1.67 × 10-24 grams. Scientists arbitrarily define this amount of mass as one atomic mass unit (amu) or one Dalton
- 8ElectronsElectrons are much smaller in mass than protons, weighing only 9.11 × 10-28 grams, or about 1/1800 of an atomic mass unit. Hence, they do not contribute much to an element’s overall atomic mass
- 9Charges in an atomsElectrons that are neutrally charged have the same number of protons and electrons.
- 10Gold foil experiment conclusionAccounting for the sizes of protons, neutrons, and electrons, most of the volume of an atom—greater than 99 percent—is, in fact, empty space.
- 11why so-called solid objects do not just pass through one another.The reason they do not is that the electrons that surround all atoms are negatively charged and negative charges repel each other.
- 12Atomic number vs mass numberThe number of protons determines an element’s atomic number and is used to distinguish one element from another. The number of neutrons is variable, resulting in isotopes, which are different forms of the same atom that vary only in the number of neutrons they possess. Together, the number of protons and the number of neutrons determine an element’s mass number
- 13Average atomic massatomic mass, which is the calculated mean of the mass number for its naturally occurring isotopes. Often, the resulting number contains a fraction.
- 14IsotopeIsotopes are different forms of an element that have the same number of protons but a different number of neutrons. Some elements—such as carbon, potassium, and uranium—have naturally occurring isotopes.
- 15Radioactive isotopesSome isotopes may emit neutrons, protons, and electrons, and attain a more stable atomic configuration (lower level of potential energy); these are radioactive isotopes, or radioisotopes. Radioactive decay (carbon-14 losing neutrons to eventually become carbon-12) describes the energy loss that occurs when an unstable atom’s nucleus releases a particle.
- 16Carbon datingCarbon-14 (14C) is a naturally occurring radioisotope that is created in the atmosphere from atmospheric 14N (nitrogen) by the addition of a neutron and the loss of a proton because of cosmic rays. This is a continuous process.
As a living organism incorporates 14C initially as carbon dioxide fixed in the process of photosynthesis, the relative amount of 14C in its body is equal to the concentration of 14C in the atmosphere. When an organism dies, it is no longer ingesting 14C, so the ratio between 14C and 12C will decline as 14C decays gradually to 14N by a process called beta decay—the emission of electrons or positrons. This decay gives off energy in a slow process. - 17Carbon dating process2After approximately 5,730 years(half-life), half of the starting concentration of 14C will have been converted back to 14N. Comparing the ratio of the 14C concentration found in an object to the amount of 14C detected in the atmosphere. the age of the material .Other elements have isotopes with different half lives. For example, 40K (potassium-40) has a half-life of 1.25 billion years, and 235U (Uranium 235) has a half-life of about 700 million years.
- 18Periodic table structurethe table groups elements that, although unique, share certain chemical properties with other elements.
elements are organized and displayed according to their atomic number - 19Chemical reactivitychemical reactivity, the ability to combine and to chemically bond with each other
- 20Periodic table rowsThere are 7 rows in the periodic table. These rows correspond to the number of shells that the elements within that row have.
- 21Columns in periodic tableThe periodic table is arranged in columns and rows based on the number of electrons and where these electrons are located.
- 22octet ruleTo achieve greater stability, atoms will tend to completely
- 23moleculesMolecules are simply two or more atoms chemically bonded together. Their electrons, which form the outermost region of each atom, come together first as the atoms form a chemical bond.
- 24Bohrs model of the atomThe Bohr model shows the atom as a central nucleus containing protons and neutrons, with the electrons in circular orbitals at specific distances from the nucleus.
These orbits form electron shells or energy levels; designated by a number and the symbol “n.”
Electrons can exist only on certain energy levels. - 25Hund's ruleIf there are multiple orbitals of equal energy, they will be filled with one electron in each energy level before a second electron is added.
Electrons tend to spread away from each other and occupy farthest place. - 26aufbau's principleAufbau's principle: Electrons fill orbitals in a consistent order: they first fill the orbitals closest to the nucleus, then they continue to fill orbitals of increasing energy further from the nucleus.
- 27Noble GasesThe group 18 atoms helium (He), neon (Ne), and argon (Ar) all have filled outer electron shell; they are highly stable as single atoms. Their non-reactivity has resulted in their being named the inert gases (or noble gases).
- 28Alkali MetalsGroup 1 elements in the left-hand column. These elements, including hydrogen (H), lithium (Li), and sodium (Na), all have one electron in their outermost shells. Hydrogen isn't as similar to the alkali metals because it can share it's electrons.
- 29HalogensGroup 17 elements, including fluorine and chlorine, have seven electrons in their outmost shells, so they tend to fill this shell with an electron from other atoms or molecules.
- 30Group 14Group 14 elements, of which carbon is the most important to living systems, have four electrons in their outer shell allowing them to make several covalent bonds (discussed below) with other atoms
- 31Electron orbitalsThese relatively complex shapes result from the fact that electrons behave not just like particles, but also like waves. Mathematical equations from quantum mechanics known as wave functions can predict within a certain level of probability where an electron might be at any given time.
- 32Electron orbitalsThe area where an electron is most likely to be found is called its orbital.
- 33SubshellsWithin each electron shell are subshells, and each subshell has a specified number of orbitals containing electrons. Subshells are designated by the letter s, p, d, and f.
- 34S and P subshellsThe s subshell is spherical in shape and has one orbital. Principal shell 1n has only a single s orbital, which can hold two electrons. Principal shell 2n has one s and one p subshell, and can hold a total of eight electrons. The p subshell has three dumbbell-shaped orbitals
- 35electron configurationThe form of the electrons present in every shell and level in an atom
- 36Chemical ReactionsAtoms undergo chemical reactions that form and break bonds to form new substances.
- 37Reversible reactionsReversible reactions are those that can go in either direction. In reversible reactions, reactants are turned into products, but when the concentration of product goes beyond a certain threshold (characteristic of the particular reaction), some of these products will be converted back into reactants; at this point, the designations of products and reactants are reversed.
- 38Chemical equillibrium in reactionsThis back and forth continues until a certain relative balance between reactants and products occurs—a state called equilibrium
- 39CationsCations are positive ions that are formed by losing electrons
- 40AnionNegative ions are formed by gaining electrons and are called anions. Anions are designated by their elemental name being altered to end in “-ide”
- 41Ionic bondsIonic bonds are formed between ions with opposite charges.
- 42Electrolyteselectrolytes (including sodium, potassium, and calcium), ions necessary for nerve impulse conduction, muscle contractions and water balance.
Many sports drinks and dietary supplements provide these ions to replace those lost from the body via sweating during exercise. - 43Covalent Bondssharing of electrons between atoms to form covalent bonds.
- 44Single, double, triple bondsOne, two, or three pairs of electrons may be shared, making single, double, and triple bonds, respectively. The more covalent bonds between two atoms, the stronger their connection. Thus, triple bonds are the strongest.
- 45Why isn't life based on nitrogen?The strength of different levels of covalent bonding is one of the main reasons living organisms have a difficult time in acquiring nitrogen for use in constructing their molecules, even though molecular nitrogen, N2, is the most abundant gas in the atmosphere. Molecular nitrogen consists of two nitrogen atoms triple bonded to each other and, as with all molecules, the sharing of these three pairs of electrons between the two nitrogen atoms allows for the filling of their outer electron shells, making the molecule more stable than the individual nitrogen atoms. This strong triple bond makes it difficult for living systems to break apart this nitrogen in order to use it as constituents of proteins and DNA.
- 46Polar covalent bondsthe electrons are unequally shared by the atoms and are attracted more to one nucleus than the other. Because of the unequal distribution of electrons between the atoms of different elements, a slightly positive (δ+) or slightly negative (δ–) charge develops.
- 47Electronegativitythe atom’s relative electronegativity contributes to the development of partial charges whenever one element is significantly more electronegative than the other
- 48Non polar covalent bondsNon polar covalent bonds form between two atoms of the same element or between different elements that share electrons equally. Examples: diatomic molecules, CH4,
- 49why is water polar while carbon dioxide nonpolarWhether a molecule is polar or nonpolar depends both on bond type and molecular shape. Both water and carbon dioxide have polar covalent bonds, but carbon dioxide is linear, so the partial charges on the molecule cancel each other out.
- 50van der Waals interactions.Weaker bonds can also form between molecules. Two weak bonds that occur frequently are hydrogen bonds and van der Waals interactions.
- 51Hydrogen BondsBecause the hydrogen is slightly positive, a weak interaction occurs between the δ+of the hydrogen from one molecule and the δ– charge on the more electronegative atoms of another molecule, usually oxygen or nitrogen. This interaction is called a hydrogen bond. This type of bond is common and occurs regularly between water molecules.
- 52London Dispersion Forcesvan der Waals interactions are weak attractions or interactions between molecules. Can occur between any two or more molecules and are dependent on slight fluctuations of the electron densities, which are not always symmetrical around an atom. For these attractions to happen, the molecules need to be very close to one another. These bonds—along with ionic, covalent, and hydrogen bonds—contribute to the three-dimensional structure of the proteins in our cells that is necessary for their proper function.
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- ap exam Biology (Biochemistry) Karteikarten am Building blocks basics , erstellt von Memo amro am 17/07/2015.
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