Biology 2.1

A total of how many elements have been defined?

118 elements have been defined; however, only 92 occur naturally, and fewer than 30 are found in living cells

How many rows are on the periodic table?

7 rows

Through the use of carbon dating, what can scientists do?

can reconstruct the ecology and biogeography of organisms living within the past 50,000 years.

chemical bonds

interactions between two or more of the same or different elements that result in the formation of molecules.

what are the four types of bonds or interactions:

ionic, covalent, hydrogen bonds, and van der Waals interactions.

Although each element has the same number of shells..?

not all of the shells are completely filled with electrons.

polar covalent bond

, the electrons shared by the atoms spend more time closer to one nucleus than to the other nucleus. Because of the unequal distribution of electrons between the different nuclei, a slightly positive (δ+) or slightly negative (δ-) charge develops.

Why does each ion has a net charge?

Because the number of electrons does not equal the number of protons

what is one way to determine the number of neutrons?

By subtracting the atomic number from the mass number.

These bonds form when an electron is shared between two elements and are the strongest and most common form of chemical bond in living organisms.

Covalent bonds

This type of bond (hydrogen bond) is common; for example, the liquid nature of water is caused by the hydrogen bonds between water molecules

Hydrogen bonds

Hydrogen has one electron; therefore, it what?

It has only one spot occupied within the lowest shell.

At its most fundamental level, life is made up of what?

Made of matter.

Carbon-14 (14C) is a naturally?

Occurring radioisotope that is created in the atmosphere by cosmic rays.

What mass and charge does a neutron have?

They have a mass of 1 and no charge. The positive (protons) and negative (electrons) charges balance each other in a neutral atom, which has a net zero charge.

a weak interaction occurs between the δ+ charge of the hydrogen atom of one molecule and the δ- charge of the other molecule. This interaction is called a

This interaction is called a hydrogen bond.

What will atoms do to become stable?

To achieve greater stability, they will tend to completely fill their outer shells and will bond with other elements to accomplish this goal by sharing electrons, accepting electrons from another atom, or donating electrons to another atom. Because

What is an ion?

When an atom does not contain equal numbers of protons and electrons

What is the periodic table of elements?

Where the elements are arranged. It is a a chart of the elements that includes the atomic number and relative atomic mass of each element. The periodic table also provides key information about the properties of elements (Figure 2.2)—often indicated by color-coding. The arrangement of the table also shows how the electrons in each element are organized and provides important details about how atoms will react with each other to form molecules.

Because protons and neutrons each have a mass of 1, the mass of an atom is equal to the number of?

a number of protons and neutrons of that atom. The number of electrons does not factor into the overall mass, because their mass is so small.

When polar covalent bonds containing a hydrogen atom form, the hydrogen atom in that bond has a

a slightly positive charge. This is because the shared electron is pulled more strongly toward the other element and away from the hydrogen nucleus. Because

Not all elements have enough electrons to fill their outermost shells, but an atom is at its most stable when?

all of the electron positions in the outermost shell are filled.

Because positive and negative charges attract, these ions stay together and form what?

an ionic bond, or a bond between ions.

Negative ions are formed by gaining electrons and are called

anions.

What are Isotopes?

are different forms of the same element that have the same number of protons, but a different number of neutrons.

Two weak bonds that occur frequently are

are hydrogen bonds and van der Waals interactions. These bonds give rise to the unique properties of water and the unique structures of DNA and proteins.

What are the remaining 26 elements?

are unstable and, therefore, do not exist for very long or are theoretical and have yet to be detected.

Hydrogen atoms cannot be what?

broken down into anything smaller while still retaining the properties of hydrogen. If a hydrogen atom were broken down into subatomic particles, it would no longer have the properties of hydrogen.

Positive ions are formed by losing electrons and are called

cations.

Each element is designated by its what?

chemical symbol (such as H, N, O, C, and Na), and possesses unique properties. These unique properties allow elements to combine and to bond with each other in specific ways.

Helium has two electrons; therefore, it can what?

completely fill the lowest shell with its two electrons.

what do the periodic table rows correspond to?

correspond to the number of shells that the elements within that row have.

The hydrogen and oxygen atoms that combine to form water molecules are bound together by?

covalent bonds.

Hydrogen bonds can form between

different molecules and they do not always have to include a water molecule. Hydrogen atoms in polar bonds within any molecule can form bonds with other adjacent molecules. For example, hydrogen bonds hold together two long strands of DNA to give the DNA molecule its characteristic double-stranded structure. Hydrogen bonds are also responsible for some of the three-dimensional structure of proteins.

This movement of electrons from one element to another is referred to as

electron transfer

All matter is composed of what?

elements

Electrons exist at what?

energy levels that form shells around the nucleus. The closest shell can hold up to two electrons.

The closest shell to the nucleus is always what?

filled first, before any other shell can be filled.

How do covalent bonds form?

form between the elements that make up the biological molecules in our cells. Unlike ionic bonds, covalent bonds do not dissociate in water.

Nonpolar covalent bonds

form between two atoms of the same element or between different elements that share the electrons equally.

Because of these vacancies in the outermost shells, we see the formation of ?

formation of chemical bonds,

Because the half-life of 14C is long, it is used to age?

formerly living objects, such as fossils.

The elements within a particular row have increasing numbers of electrons as the columns proceed ?

from left to right.

Negative ions are formed by

gaining electrons

How elements interact with one another depends on?

how their electrons are arranged and how many openings for electrons exist at the outermost region where electrons are present in an atom. Electrons

give water the unique properties that sustain life. If it were not for hydrogen bonding, water would be a gas rather than a liquid at room temperature.

hydrogen bond

What is a electron and where does it reside?

is a negatively charged particle that travels in the space around the nucleus. it resides outside of the nucleus. It has a negligible mass and has a charge of -1.

What is a proton?

is a positively charged particle that resides in the nucleus (the core of the atom) of an atom and has a mass of 1 and a charge of +1.

hydrogen (H), is the exception because?

is made of one proton and one electron.

The time it takes for half of the original concentration of an isotope to decay to its more stable form is called what?

its half-life.

Where do neutrons reside?

like protons, reside in the nucleus of an atom.

Positive ions are formed by

losing electrons

What is each Each element made of?

made of atoms, each with a constant number of protons and unique properties.

The mass number, or atomic mass, is the number of what?

number of protons plus the number of neutrons of that element.

What does matter occupy?

occupies space and has mass.

There are two types of covalent bonds:

polar and nonpolar.

The covalent bonds between hydrogen and oxygen atoms in water are

polar covalent bonds. The shared electrons spend more time near the oxygen nucleus, giving it a small negative charge, than they spend near the hydrogen nuclei, giving these molecules a small positive charge.

All atoms contain??

protons, electrons, and neutrons

An atom is the smallest component of an element that what?

retains all of the chemical properties of that element. For example, one hydrogen atom has all of the properties of the element hydrogen, such as it exists as a gas at room temperature, and it bonds with oxygen to create a water molecule.

Carbon-14 contains what?

six protons and eight neutrons. Therefore, it has a mass number of 14 (six protons and eight neutrons) and an atomic number of 6, meaning it is still the element carbon.

Carbon-12, the most common isotope of carbon, it contains?

six protons and six neutrons. Therefore, it has a mass number of 12 (six protons and six neutrons) and an atomic number of 6 (which makes it carbon).

Some isotopes happen to be what?

some are unstable and will lose protons, other subatomic particles, or energy to form more stable elements. These are called radioactive isotopes or radioisotopes.

What is a element?

substances that cannot be broken down or transformed chemically into other substances.

What elements have naturally occurring isotopes?

such as carbon, potassium, and uranium, have naturally occurring isotopes.

A the nucleus is the?

the core of the atom

The atomic number of an element is equal to?

the number of protons that element contains.

If you look at the periodic table, you will see that hydrogen and helium are what?

the only two elements in the first row. This is because they only have electrons in their first shell. Hydrogen and helium are the only two elements that have the lowest shell and no other shells.

What is the ocet rule

the outermost shells of the elements with low atomic numbers (up to calcium, with atomic number 20) can hold eight electrons

In multicellular organisms, such as animals, molecules can interact to form cells that combine to form what?

to form tissues, which make up organs. These combinations continue until entire multicellular organisms are formed.

van der Waals interactions are

weak attractions or interactions between molecules. They occur between polar, covalently bound, atoms in different molecules. Some of these weak attractions are caused by temporary partial charges formed when electrons move around a nucleus.