Chapter 2 Flashcards
Matter is defined as?
Anything that takes up space and that has mass
The smallest chemical units of matter are?
Atoms
A nucleus is composed of? What is an exception?
Uncharged neutrons and positively charged protons.
The only exception is the nucleus of a normal hydrogen atom, which is composed of only a single proton and no neutrons.
Where can you find electrons in an atom?
Orbiting the nucleus
The number of electrons in an atom typically equals?
The number of protons, so overall atoms are electrically neutral
What is an element?
Matter that is composed of a single type of atom. For example, gold is an element because it consists of only gold atoms. In contrast, the ink in your pen is not an element, because it is composed of many different kinds of atoms
How do elements differ from one another?
In their atomic number, which is the number of protons in their nuclei. For example, the atomic number of hydrogen, carbon, and oxygen are 1, 6, and 8, respectively, because all hydrogen nuclei contain a single proton, all carbon nuclei have six protons, and all oxygen nuclei have 8 protons
What is the atomic mass of an atom?
Sometimes called its atomic weight, it is the sum of the masses of its protons, neutrons, and electrons
Protons and neutrons each have a mass of what?
Electron?
Of approximately 1 atomic mass unit, which is also called a dalton.
An electron is much less massive, with a mass of about 0.00054 dalton.
Why are electrons often ignored in discussions of atomic mass?
Because their contribution to the overall mass is negligible, therefore the sum of the number of protons and neutrons approximates the atomic mass of an atom
There are ___ naturally occurring elements known, however organisms typically utilize only about ___ elements, each of which has its own symbol that is derived from its English or Latin name
93
20
Every atom of an element has the same number of protons, but atoms of a given element can differ in the number of? What is it called?
Neutrons in their nuclei which are called isotopes. For example there are three naturally occurring isotopes of carbon, each having six protons and six electrons
Over ___% of carbon atoms also have six neutrons. Because these atoms have six protons and six neutrons, the atomic mass of this isotope is about ___ daltons, and it is known as carbon-__, symbolized as ____
95%
12 daltons
carbon-12
12^C
Atoms of carbon 13 have how many neutrons?
Atoms of carbon 14 have how many neutrons? Why is carbon 14 unstable?
carbon-13 have7 neutrons per nucleus
Carbon-14 have 8 neutrons per nucleus. Unlike the first two isotopes, the nucleus of 14^C is unstable because of the ratio of its protons and neutrons
What do unstable atomic nuclei release?
Energy and subatomic particles such as neutrons, protons, and electrons in a process called radioactive decay.
Atoms that undergo radioactive decay are called?
Radioactive isotopes
Radioactive decay and radioactive isotopes play important roles in?
Microbiological research, medical diagnosis, the treatment of disease, & the complete destruction of contaminating microbes (sterilization) of medical equipment and chemicals
Although the nuclei of atoms determine their identities, it is what the determines an atoms chemical behavior? Why?
Electrons because the nuclei of different atoms almost never come close enough together to interact. Typically only the electrons of atoms interact. Thus, because all of the isotopes of carbon (for example) have the same number of electrons, all these isotopes behave the same way in chemical reactions, even though their nuclei are different.
An electron shell depicts?
The probable locations of electrons at a given time
Each electron shell can hold how many electrons?
Only a certain maximum number of electrons. For example the first shell can accommodate a maximum of 2 electrons, and the second shell can hold no more than 8 electrons.
Electrons in the outermost shell of atoms are called?
Valence electrons
Outer electron shells are stable when they contain how many electrons (except for the first electron shell, which is stable with only ___ electrons, because that is the maximum number)
8
2
When atoms’ outer shells are not filled with eight electrons, they either?
Have room for more electrons or have “extra” electrons, depending on whether it is easier for them to gain electrons or lose electrons. For example, an oxygen atom with 6 electrons in its outer shell has 2 unfilled spaces, because it requires less energy for the atom to gain two electrons than to lose 6 electrons. A calcium atom by contrast, has two “extra” electrons in its outer (fourth) shell, because it requires less energy to lose these two electrons than to gain 6 new ones. When a calcium atom loses two electrons, its third shell, which is then its outer shell, is full and stable with eight electrons
An atom’s outermost electrons are called valence electrons, & thus the outermost shell of an atom is the?
Valence shell
An atom’s valence, defined as its combining capacity, is considered to be positive if? Negative if? Give calcium as an example
Positive if its valence shell has extra electrons to give up
Negative if its valence shell has spaces to fill
Thus a calcium atom, with two electrons in its valence shell, has a valence of +2, whereas an oxygen atom, with 2 spaces to fill in its valence shell, has a valence of -2
Atoms combine with one another by? What is this called?
Either sharing or transferring valence electrons in such a way as to fill their valence shells.
Such interactions between atoms are called chemical bonds
Define molecule and compound. Give two hydrogen atoms bonded together and two hydrogen and an oxygen (water) as an example.
Molecule- Two or more atoms held together by chemical bonds form a molecule.
Compound- A molecule that contains atoms of more than one element is a compound.
Two hydrogen atoms bonded together form a hydrogen molecule, which is NOT a compound because only one element is involved. However, two hydrogen atoms bonded to an oxygen atom form a molecule of water which is a compound
What is a covalent bond? Give two hydrogen as an example and two oxygen.
The sharing of a pair of electrons by two atoms.
Each hydrogen atom consists of a single proton orbited by a single electron. Because the valence shell of each hydrogen atom requires two electrons to be filled, each atom shares its single electron with the other, forming a hydrogen molecule in which both atoms have full shells.
Two oxygen atoms can share electrons but they must share two pairs of electrons for their valence shells to be full. Because two pairs of electrons are involved, oxygen atoms form two covalent bonds, or a double covalent bond with one another.
What is electronegativity?
The attraction of an atom for electrons
The more an atom is electronegative (attraction of an atom for electrons) the greater the?
Pull its nucleus exerts on electrons
Electronegativities tend to increase from left to right in the periodic table. The reason for this is?
Electronegativities of elements decrease from top to bottom in the chart because?
Increase from left to right because elements towards the right of the chart have more protons and thus exert a greater pull on electrons.
Decrease from top to bottom because the distance between the nucleus and the valence shell increases as elements get larger
Atoms with equal or nearly equal electronegativities, such as two hydrogen atoms or a hydrogen and a carbon, share electrons?
Equally or nearly equally
What are “poles”?
Opposed forces. Atoms with similar electronegativites, the shared electrons tend to spend an equal amount of time around each nucleus of the pair, and no pole exist; therefore, the bond between them is a nonpolar covalent bond
An example of structural formula for two shared hydrogen atoms
1) H — H and 2) H:H
1) In the first symbol, the dash represents the chemical bond between the atoms.
2) In the second symbol, the dots represent the electron pair of the covalent bond.
These are known as structural formulas
An example of molecular formula for hydrogen
H2 The subscript 2 indicates the number of hydrogen atoms that are bonded, not the number of shared electrons
A line in the structural formula represents?
A double line in the structural formula represents?
Single line- Covalent bond formed from the sharing of two electrons.
Double line- indicates the sharing of 4 electrons
How are carbon atoms critical to life?
Because a carbon atom has 4 electrons in its valence shell, it has equal tendency to either lose or gain 4 electrons. Either event produces a full outer shell. The result is that carbon atoms tend to share electrons and form four covalent bonds with one another, and with many other types of atoms. Each carbon atom in effect acts as a four-way intersection where different components of a molecule can attach. One result of this feature is that carbon atoms can form very large chains that constitute the “backbone” of many biological important molecules. Carbon chains can be branched or unbranched, and some even close back on themselves to form rings.
What are organic compounds?
Compounds that contain carbon and hydrogen atoms. Among the many biological important organic compounds are proteins and carbohydrates.
What happens if two covalently bound atoms have significantly different electronegativities?
Their electrons will not be shared equally. Instead, the electron pair will spend more time orbiting the nucleus of the atom with greater electronegativity. This type of bond, in which there is unequal sharing of electrons, is a polar covalent bond
Is water a polar or non polar covalent bond?
Water is a polar covalent bond, there is unequal sharing of electron pairs. Because oxygen is more electronegative than hydrogen, the electrons spend more time near the oxygen nucleus than near the hydrogen nuclei, and thus the oxygen atom acquires a transient (partial) negative charge. The hydrogen nuclei each have a corresponding transient positive charge. The covalent bond between an oxygen atom & a hydrogen atom is called polar because the atoms have opposite partial electrical charges.
Generally, molecules with polar covalent bonds are?
Water soluble, and nonpolar molecules are not.
The most important polar covalent bonds for life are those that involve?
Hydrogen because they allow hydrogen bonding
Both nonpolar and polar covalent bonds form?
Angles between atoms such that the distances between electron orbits are maximized
What is an ion?
An atom or group of atoms that has either a full negative charge or a full positive charge. (One atom loses an electron and one atom gains electrons, no sharing)
What are cations?
Positively charged ions
What are anions?
Negatively charged ions
What is an ionic bond?
Cations and anions attract each other because of their opposite charge. They form crystalline compounds composed of metallic and nonmetallic ions known as salts, such as sodium chloride (NaCl), & potassium chloride (KCl)
How do ionic bonds differ from covalent bonds?
Ions do not share electrons. Instead, the bond is formed from the attraction of opposite electrical charges
How does water molecules interfere with ionic bonds of salts?
The polar bonds of water molecules interfere with the ionic bonds of salts, causing dissociation (also called ionization). This occurs as the partial negative charge on the oxygen atom of water attracts cations, & the partial positive charge on hydrogen atoms attracts anions.
What are electrolytes?
When cations and anions disassociates from one another & become surrounded by water molecules (are hydrated), they are called electrolytes because they can conduct electricity through the solution. Electrolytes are critical for life because they stabilize a variety of compounds, act as electron carriers, & allow electrical gradients to exist within cells.
Electrons are shared between atoms in ________ bonds and transferred from one atom to another in ________ bonds
Shared- covalent
Transferred- ionic
Hydrogen atoms bind to oxygen atoms by means of?
Polar covalent bonds, which results in transient positive charges on the hydrogen atoms. Hydrogen atoms form polar covalent bonds with atoms of other elements as well.
Describe a hydrogen bond
The electrical attraction between a partially charged hydrogen atom and full or partial negative charge on either a different region of the same molecule or another molecule.
Hydrogen bonds can be likened to weak ionic bonds in that they?
Arise from the attraction of positive and negative charges. Although they are a consequence of polar covalent bonds between hydrogen atoms and other, more electronegative atoms, hydrogen bonds themselves are not covalent bonds- They do not involve the sharing of electrons.
Covalent bonds are essential for life because they strongly link atoms together to form molecules. Hydrogen bonds, though weaker than covalent bonds, are also essential. The cumulative effect of numerous hydrogen bonds is to?
Stabilize the three-dimensional shapes of large molecules. For example, the familiar double helix shape of DNA is due in part to the stabilizing effects of thousands of hydrogen bonds holding the molecule together. Exact shape is critical for the functioning of enzymes, antibodies, intercellular chemical messengers, & the recognition of target cells by pathogens.
Because hydrogen bonds are weak, they can be overcome when necessary. For example, the two complementary halves of a DNA molecule are held together primarily by hydrogen bonds, & they can be separated for?
DNA replication and other processes
Scientists define chemical reactions as?
The making or breaking of such chemical bonds
All chemical reactions begins with?
All chemical reactions results in?
Reactants, the atoms, ions, or molecules that exist at the beginning of a reaction.
Results in products, the atoms, ions, or molecules left after the reaction is complete
Biochemistry involves?
The chemical reactions of living things
Reactants and products may have very different physical and chemical characteristics. For example, hydrogen & oxygen are gases and have very different properties of?
Water, which is composed of hydrogen & oxygen atoms.
The numbers and types of atoms never change in a?
Chemical reaction; atoms are neither destroyed nor created, only rearranged.
Three general categories of biochemical reactions (reactions that occur in organisms)
1) Synthesis
2) Decomposition
3) Exchange reactions
Synthesis reactions involve?
The formation of larger, more complex molecules. Synthesis reactions can be expressed symbolically as: Reactant + Reactant —-> Product(s)
The arrow indicates the direction of the reaction & the formation of new chemical bonds
What is dehydration synthesis?
Two smaller molecules are joined together by a covalent bond, and a water molecule is also formed.
The word dehydration in this reaction refers to the fact that one of the products is a water molecule formed when a hydrogen ion from one reactant combines with a hydroxyl ion from another reactant.
Synthesis reactions require energy to?
Break bonds in the reactants & to form new bonds to make products.
What are endothermic reactions?
Reactions that require energy because they trap energy within new molecular bonds.
What is anabolism?
Taken together, all of the synthesis reactions in an organism
What are decomposition reactions?
The reverse of synthesis reactions in that they break bonds within larger molecules to form smaller atoms, ions, and molecules. These reactions release energy and are therefore exothermic
Decomposition reactions can be represented by the following formula
Reactant —–> Product + Product
Reactions that release energy
Exothermic
Synthesis and decomposition reactions are often reversible in?
Living things
Hydrolysis is what type of reaction?
A common type of decomposition reaction in biochemistry. It is the reverse of dehydration synthesis. In these reactions a covalent bond in a large molecule is broken, & the ionic components of water are added to the products
What is catabolism?
All of the decomposition reactions in an organism
What are exchange reactions (also called transfer reactions)?
Have features similar to both synthesis and decomposition reactions. They involve breaking and forming covalent bonds, & they involve both endothermic & exothermic steps. Atoms are moved from one molecule to another. These reactions can be represented as either:
A + BC —> AB + C OR AB + CD ——> AD + BC
