Atoms, elements and compounds Flashcards
Revision notes (29 cards)
Can you describe the differences between elements, compounds and mixtures
Elements:
Elements are pure substances made up of only one type of atom.
They cannot be broken down into simpler substances by chemical means.
Each element has its own unique properties and is represented by a chemical symbol (e.g., H for hydrogen, O for oxygen).
Compounds:
Compounds are substances composed of two or more different elements chemically combined in fixed proportions.
They can be broken down into simpler substances (elements) by chemical reactions.
Compounds have properties different from the elements they are composed of.
Examples include water (H2O), carbon dioxide (CO2), and sodium chloride (NaCl).
Mixtures:
Mixtures are composed of two or more substances physically mixed together.
The substances in a mixture retain their own properties and can be separated by physical means (e.g., filtration, distillation).
Mixtures can vary in composition and properties depending on the amounts of each substance present.
Examples include air (a mixture of gases), saltwater (a mixture of salt and water), and salad (a mixture of various vegetables).
Describe the structure of the atom as a central
nucleus containing neutrons and protons
surrounded by electrons in shells
Atoms have a central nucleus made of neutrons (neutral) and protons (positive), surrounded by electrons (negative) arranged in energy levels or shells.
State the relative charges and relative masses of
a proton, a neutron and an electron
Proton: Positive charge, Relative mass of 1.
Neutron: No charge (neutral), Relative mass of 1.
Electron: Negative charge, Negligible mass (very light compared to protons and neutrons).
Define proton number/ atomic number as the
number of protons in the nucleus of an atom
The number of protons in the nucleus of an atom determines its proton number or atomic number.
Define mass number/nucleon number as the
total number of protons and neutrons in the
nucleus of an atom
The total number of protons and neutrons in the nucleus of an atom is called the mass number or nucleon number.
Determine the electronic configuration of
elements and their ions with proton number 1 to
20
The arrangement of electrons in the energy levels or shells around the nucleus of an atom. For example, hydrogen has 1 electron, so its electronic configuration is 1. Helium has 2 electrons, so its electronic configuration is 2. Neon has 10 electrons, so its electronic configuration is 2,8.
Can you state the following?
(a) Group VIII noble gases have a full outer shell.
(b) The number of outer shell electrons is equal to the group number in Groups I to VII.
(c) The number of occupied electron shells is equal to the period number.
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Define isotopes as different atoms of the same
element that have the same number of protons
but different numbers of neutrons
Isotopes are different atoms of the same element that have the same number of protons but different numbers of neutrons.
Interpret and use symbols for atoms,
Atom symbols consist of the element’s mass number (total number of protons and neutrons) as a superscript and its proton number (atomic number) as a subscript. For example, carbon-12 (12^6C) has 6 protons and 6 neutrons.
Ions are atoms that have gained or lost electrons, indicated by a superscript indicating the charge. For example, chloride ion (Cl-) has gained one electron and is represented as 35^17Cl^–.
State that isotopes of the same element have
the same chemical properties because they have
the same number of electrons and therefore the
same electronic configuration
Isotopes of the same element have the same chemical properties because they have the same number of electrons and, therefore, the same electronic configuration.
Calculate the relative atomic mass of an element
from the relative masses and abundances of its
isotopes
The relative atomic mass of an element is calculated by considering the relative masses and abundances of its isotopes.
It is calculated using the weighted average of the isotopic masses, weighted by their relative abundances.
For example, if an element has two isotopes with masses 10 and 12 and abundances 20% and 80% respectively, the relative atomic mass would be calculated as (10 * 0.20) + (12 * 0.80) = 11.2.
Describe the formation of positive ions, known as
cations, and negative ions, known as anions
Positive ions, called cations, form when atoms lose electrons, leading to a net positive charge.
Negative ions, known as anions, form when atoms gain electrons, resulting in a net negative charge.
State that an ionic bond is a strong electrostatic
attraction between oppositely charged ions
An ionic bond is a strong electrostatic attraction between oppositely charged ions. It forms when a cation and an anion are attracted to each other due to their opposite charges.
Describe the formation of ionic bonds between
elements from Group I and Group VII, including
the use of dot-and-cross diagrams
Group I elements, like sodium, readily lose one electron to achieve a stable electron configuration, forming a +1 cation.
Group VII elements, like chlorine, easily gain one electron to attain a stable electron configuration, forming a -1 anion.
In the formation of ionic bonds between sodium (Na) and chlorine (Cl), sodium transfers its lone outer electron to chlorine, resulting in the formation of Na+ and Cl- ions.
Describe the properties of ionic compounds:
(a) high melting points and boiling points
(b) good electrical conductivity when aqueous or
molten and poor when solid
(a) Ionic compounds typically have high melting and boiling points due to the strong electrostatic forces of attraction between ions in the solid state.
(b) Ionic compounds conduct electricity well when dissolved in water (aqueous) or melted because their ions are free to move and carry electric charge. However, they are poor conductors of electricity when solid because their ions are fixed in a lattice structure and cannot move.
Describe the giant lattice structure of ionic
compounds as a regular arrangement of
alternating positive and negative ions
Ionic compounds possess a giant lattice structure, characterized by a regular arrangement of positively charged cations and negatively charged anions, alternating in a three-dimensional pattern.
Describe the formation of ionic bonds between
ions of metallic and non-metallic elements,
including the use of dot-and-cross diagrams
Metallic elements, such as sodium, lose electrons to become cations, while non-metallic elements, such as chlorine, gain electrons to form anions.
For example, in the formation of sodium chloride (NaCl), sodium loses an electron to chlorine, resulting in the formation of Na+ and Cl- ions.
Explain the following:
Explain in terms of structure and bonding the
properties of ionic compounds:
(a) high melting points and boiling points
(b) good electrical conductivity when aqueous or
molten and poor when solid
Covalent bonding
Covalent bonds form when a pair of electrons is shared between two atoms, allowing both atoms to achieve noble gas electronic configurations.
Describe the formation of covalent bonds in
simple molecules, including H2, Cl 2, H2O, CH4,
NH3 and HCl. Use dot-and-cross diagrams to
show the electronic configurations in these and
similar molecules
H2: Each hydrogen atom shares its single electron with the other, forming a single covalent bond.
Cl2: Each chlorine atom shares one of its outer electrons with the other, forming a single covalent bond.
H2O: Oxygen shares two electrons, one from each hydrogen atom, forming two covalent bonds.
CH4: Carbon shares one electron with each of the four hydrogen atoms, forming four covalent bonds.
NH3: Nitrogen shares three electrons, one from each hydrogen atom, forming three covalent bonds.
HCl: Hydrogen shares one electron with chlorine, forming a single covalent bond.
Dot-and-cross diagrams can be drawn to illustrate the sharing of electrons in these molecules.
the structure and bonding the
properties of simple molecular compounds
(a) low melting points and boiling points
(b) poor electrical conductivity
Describe the formation of covalent bonds in
simple molecules, including CH3OH, C2H4, O2,
CO2 and N2. Use dot-and-cross diagrams to show
the electronic configurations in these and similar
molecules
Formation of Covalent Bonds in Additional Simple Molecules:
CH3OH: Carbon shares electrons with three hydrogen atoms and one oxygen atom, forming covalent bonds.
C2H4: Two carbon atoms share electrons with each other and with two hydrogen atoms each, forming covalent bonds.
O2: Two oxygen atoms share two pairs of electrons, forming a double covalent bond.
CO2: Carbon shares electrons with two oxygen atoms, forming double covalent bonds.
N2: Two nitrogen atoms share three pairs of electrons, forming a triple covalent bond.
Explain in terms of structure and bonding the
properties of simple molecular compounds
(a) low melting points and boiling points in
terms of weak intermolecular forces (specific
types of intermolecular forces are not
required)
(b) poor electrical conductivity
Describe the giant covalent structures of graphite and diamond
Graphite: Consists of layers of carbon atoms arranged in hexagonal rings. Each carbon atom forms three covalent bonds with other carbon atoms within the layer, creating a flat, two-dimensional structure.
Diamond: Each carbon atom in diamond forms four strong covalent bonds with other carbon atoms in a tetrahedral arrangement, creating a three-dimensional network structure.
