2.1: Atoms, Isotopes, Ions, and Molecules

What determines the properties of elements, molecules, and matter?

Atomic structure determines the properties of elements, molecules, and matter.

What is matter?

Matter is anything that occupies space and has mass.

How many naturally occurring elements are there?

There are 92 naturally occurring elements.

What are atoms composed of?

Atoms consist of protons, neutrons, and electrons.

What is the most stable configuration for an atom?

Atoms are most stable when their outermost or valence electron shells contain the maximum number of electrons.

What types of bonds can electrons create between atoms?

Electrons can create ionic bonds, covalent bonds, polar covalent bonds, hydrogen bonds, and van der Waals interactions.

What are isotopes?

Isotopes are different forms of an element that have different numbers of neutrons but the same number of protons.

What is an example of a radioactive isotope?

Carbon-14 is an example of a radioactive isotope.

What is the significance of the four elements common to all living organisms?

The four elements common to all living organisms are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

How are chemical symbols for elements designated?

Chemical symbols are designated by a single capital letter or a combination of two letters, often derived from their English or Latin names.

What is the relationship between living systems and free energy?

Living systems require a constant input of free energy to grow, reproduce, and maintain dynamic homeostasis.

What is Big Idea 2 in the AP Biology Curriculum Framework?

Big Idea 2 focuses on how biological systems utilize free energy and molecular building blocks.

What is the role of data in scientific inquiry according to the AP Biology curriculum?

Students must justify the selection of data needed to answer scientific questions.

What is the total number of elements known to science?

There are 118 known elements, but only 98 occur naturally.

What happens to elements that are synthesized in laboratories?

Elements synthesized in laboratories are unstable.

What is the chemical symbol for sodium and its origin?

The chemical symbol for sodium is Na, derived from its Latin name 'natrium'.

What are the proportions of elements in living vs. non-living systems?

Elements in living organisms are found in different proportions compared to their occurrence in the non-living world.

What are the primary elements found in living organisms (humans) and their approximate percentages?

Oxygen (65%), Carbon (18%), Hydrogen (10%), Nitrogen (3%)

How does the composition of the atmosphere differ from that of the Earth's crust in terms of oxygen and nitrogen?

The atmosphere contains 21% oxygen and 78% nitrogen, while the Earth's crust contains 46% oxygen and trace amounts of nitrogen.

What is an atom?

An atom is the smallest unit of matter that retains all the chemical properties of an element.

What are the two main regions of an atom?

The nucleus (containing protons and neutrons) and the outermost region (holding electrons in orbit).

What particles make up an atom?

Atoms are composed of protons, neutrons, and electrons.

What is the charge and mass of protons and neutrons?

Protons are positively charged and have a mass of approximately 1.67 × 10^-24 grams; neutrons are uncharged and have a similar mass.

How does the mass of electrons compare to protons and neutrons?

Electrons are much smaller, weighing only 9.11 × 10^-28 grams, or about 1/1800 of an atomic mass unit.

What is the significance of neutrons in an atom?

Neutrons contribute significantly to the atom's mass but not to its charge.

How is atomic mass typically calculated?

Atomic mass is calculated based on the number of protons and neutrons, ignoring the mass of electrons.

What is the relationship between the number of protons and electrons in a neutral atom?

In neutral atoms, the number of electrons equals the number of protons, resulting in no net charge.

What is the reason that solid objects do not pass through one another?

Electrons surrounding atoms are negatively charged and repel each other, preventing solid objects from passing through.

What is the approximate percentage of empty space in an atom?

More than 99 percent of an atom's volume is empty space.

What is the common isotope of hydrogen composed of?

The most common isotope of hydrogen consists of one proton and one electron with no neutrons.

What is the role of electrons in determining an atom's charge?

Electrons contribute greatly to the atom's charge, with each electron having a negative charge equal to the positive charge of a proton.

What happens to the charges in uncharged, neutral atoms?

In uncharged atoms, the positive and negative charges cancel each other out, leading to no net charge.

What is the significance of impurities in a gold coin?

Impurities are small amounts of other elements mixed with gold atoms in a gold coin.

How do chemical reactions obey the same laws in living and non-living worlds?

All elements and the chemical reactions between them obey the same chemical and physical laws, regardless of their context.

What is the approximate percentage of carbon in the atmosphere?

Carbon is present in trace amounts in the atmosphere.

What is the approximate percentage of hydrogen in the Earth's crust?

Hydrogen is present at about 0.1% in the Earth's crust.

What is the role of the nucleus in an atom?

The nucleus contains protons and neutrons and is the central part of the atom.

What is the definition of an atomic mass unit (amu)?

An atomic mass unit (amu) is defined as approximately 1.67 × 10^-24 grams, the mass of protons and neutrons.

What are the charges and masses of protons, neutrons, and electrons?

Proton: +1 charge, 1 amu mass; Neutron: 0 charge, 1 amu mass; Electron: -1 charge, 0 amu mass.

Where are protons and neutrons located in an atom?

Both protons and neutrons are located in the nucleus.

Where are electrons located in an atom?

Electrons are located in orbitals around the nucleus.

What determines an element's atomic number?

The number of protons in an atom determines its atomic number.

How do isotopes differ from one another?

Isotopes are different forms of the same element that have the same number of protons but different numbers of neutrons.

What is the mass number of an element?

The mass number is the sum of the number of protons and neutrons in an atom.

How can you calculate the number of neutrons in an element?

Subtract the number of protons from the mass number to find the number of neutrons.

What is atomic weight?

Atomic weight is the calculated mean of the atomic weights of an element's naturally occurring isotopes.

What is the atomic mass of chlorine and why is it not a whole number?

The atomic mass of chlorine is 35.45 because it is composed of isotopes with different masses (35 and 37).

What are the stable isotopes of carbon?

The stable isotopes of carbon are carbon-12 and carbon-13.

How many neutrons does carbon-12 contain?

Carbon-12 contains 6 neutrons.

How many neutrons does carbon-13 contain?

Carbon-13 contains 7 neutrons.

What is radioactive decay?

Radioactive decay is the process by which an unstable atom's nucleus releases radiation to attain a more stable atomic configuration.

What is carbon-14 and how is it formed?

Carbon-14 is a naturally occurring radioisotope created in the atmosphere from nitrogen-14 by the addition of a neutron and loss of a proton due to cosmic rays.

What happens to the ratio of carbon-14 to carbon-12 after an organism dies?

The ratio declines as carbon-14 decays to nitrogen-14 since the organism is no longer ingesting carbon-14.

What is beta decay?

Beta decay is the emission of electrons or positrons during the decay of a radioactive isotope.

How long does it take for half of the carbon-14 in a sample to decay?

It takes approximately 5,730 years for half of the carbon-14 to decay.

What is the significance of carbon dating?

Carbon dating is used to determine the age of organic materials by measuring the ratio of carbon-14 to carbon-12.

What is the contribution of electrons to an atom's mass number?

The contribution of electrons to an atom's mass number is negligible and is typically disregarded.

What is the relationship between protons and electrons in a neutral atom?

In a neutral atom, the number of protons equals the number of electrons.

What elements are mentioned as having naturally occurring isotopes?

Carbon, potassium, and uranium are mentioned as having naturally occurring isotopes.

What is the atomic symbol for carbon?

The atomic symbol for carbon is a capital C.

What is the relative atomic mass of carbon?

The relative atomic mass of carbon is 12.011.

What is the term for the time it takes for half of the original concentration of an isotope to decay?

Half-life

Why is the half-life of Carbon-14 significant for dating objects?

It is long enough to date formerly living objects such as old bones or wood.

How can the age of a material be calculated using Carbon-14?

By comparing the ratio of Carbon-14 concentration found in an object to the amount in the atmosphere.

What is the maximum age limit for dating materials using Carbon-14?

About 50,000 years.

What is the half-life of Potassium-40?

1.25 billion years.

What is the half-life of Uranium-235?

About 700 million years.

What method do scientists use to study the age of fossils or remains of extinct organisms?

Radiometric dating.

Who devised the periodic table and in what year?

Russian chemist Dmitri Mendeleev in 1869.

What are the three physical states of elements at room temperature?

Gases, solids, or liquids.

How are elements organized in the periodic table?

According to their atomic number and shared chemical and physical properties.

What additional information does the periodic table provide for each element?

The element's atomic mass, symbol, and name.

What are the two additional rows of elements in the periodic table called?

Lanthanides and actinides.

Which elements are included in the lanthanides?

Elements 57 through 71.

Which elements are included in the actinides?

Elements 89 through 98.

What does the atomic number represent in the periodic table?

The number of protons in an atom.

What is the atomic mass in the periodic table?

The average mass of different isotopes, estimated to two decimal places.

How does the ratio of Carbon-14 to Carbon-12 in a living elephant compare to that in a pygmy mammoth?

The ratio would be the same in both the elephant and the mammoth.

What is the significance of the atomic mass of an element?

It reflects the average mass of all the isotopes of that element.

What is the role of chemical reactivity in elements?

It determines the ability of elements to combine and chemically bond with each other.

What is the atomic mass of Carbon?

12.01.

How are the elements in the periodic table arranged?

In a series of rows and columns based on shared chemical and physical properties.

What is the importance of the periodic table in chemistry?

It groups elements that share certain chemical properties, facilitating the study of their behaviors.

What happens to the ratio of Carbon-14 in an organism as it ages?

The ratio decreases as Carbon-14 decays over time.

What is the significance of isotopes in radiometric dating?

Different isotopes have unique half-lives that allow for dating materials of varying ages.

What is the atomic symbol for hydrogen?

H

What is the atomic number of hydrogen?

1

What is the atomic mass of hydrogen?

1

How does the atomic mass compare to the atomic number for most small elements?

The atomic mass is always larger than the atomic number.

What is the approximate relationship between atomic mass and atomic number for small elements?

The atomic mass is approximately double the atomic number.

What are the three categories that elements are divided into?

Metals, nonmetals, and metalloids.

Where do metalloids form a diagonal line on the periodic table?

From period two, group thirteen to period seven, group sixteen.

What type of elements are found to the left of the metalloids?

Metals.

What type of elements are found to the right of the metalloids?

Nonmetals.

What does the periodic table group elements according to?

Chemical properties.

What determines the differences in chemical reactivity between elements?

The number and spatial distribution of an atom's electrons.

What are molecules?

Two or more atoms chemically bonded together.

What is the relationship between protons and electrons in electrically neutral atoms?

The number of electrons is the same as the number of protons.

Who developed the early model of the atom in 1913?

Danish scientist Niels Bohr.

What does the Bohr model depict?

An atom as a central nucleus containing protons and neutrons, with electrons in shells at specific distances.